2. The Nature of Color

©2025 Henk ten Have, CC BY-NC 4.0 https://doi.org/10.11647/OBP.0443.02

2.1 Introduction

In Ancient Greek the word pharmakon in general refers to a tool, or means for or against something, and more specifically to a healing or deadly drug, poison, charm or spell, dye or color. The same person producing pharmaka therefore makes drugs to heal ailments and diseases but also pigments and paints. This is not surprising since many natural pigments were assumed to have medicinal properties and were used in recipes for medication. At the same time, ingredients could be healing but also poisonous. One of the most commonly applied pigments was lead white, already known in Antiquity. It is basic lead carbonate, prepared from a natural mineral, and used as paint but also cosmetic in various cultures (St Clair 2016). It is highly toxic for those manufacturing it but also for people who use it to whiten their skin. The white color it produces is seen as beautiful, charming and seducing but also intoxicating and dangerous.

As a pharmakon, color is primarily regarded as a material that covers things and beings. Color is like an envelope, a second skin that encompasses an object or body. This conception is reflected in Indo-European languages where the Latin word color is derived from the verb celare, which means to conceal. In Ancient Greek, the word for color (khroma) refers to skin or bodily surface (Pastoureau 2019). The etymology of the term and the ambivalence of color as matter has instigated many philosophers to reflect on the nature of color.

In our experience, colors are real and out there in the world. At the same time they are variable; depending on light, context and point of view we see different colors and not all observers see the same colors. To illustrate the color blue we may point to the sky, but the color of the sky changes rapidly during twilight. This changeability makes it doubtful whether the color that an object appears to have is really a property of the object or rather dependent on the perceiver. Is it true that color, as expressed in the origin of the term, is deceptive and not really part of the world as we see it? Consequently, the issue of color refers to a broader philosophical concern about the certainty of knowledge and the reliability of our senses. It also problematizes the status of scientific understanding. Science tells us that only physical facts exist in the world, and that colors should be identified with physical properties such as wavelength. When we look at the grass it looks green but from the point of view of science it has no color. Our visual experience is misleading us. But if it is an illusion that the world which we experience with our sensory organs is colored, the same is true not only for other qualitative properties such as smell, sound and taste, but also for concepts that are crucial to human existence, like agency, mind, personhood, responsibility and moral values. The subject of color has attracted the attention of philosophers since it relates to a range of philosophical issues concerning appearance and reality, subjectivity and objectivity, science and common sense, mind and matter.

In this chapter, a brief description will be provided of the main philosophical theories of color. Realism refers to a set of theories that regard color as an objective property of objects in the outside world which is independent from the perceiving subjects. Antirealist theories postulate that colors are products of the visual system and that they do not exist without perceiving subjects. Because it is typical for the experience of color to be not merely located in the outside world or in the mind, but situated between the objective and the subjective world, a third type of theory emphasizes color relationism. These theories assume that color vision is not simply detection of color but has a specific purpose, namely identification of features of the environment that are useful for the perceiving organism, helping it to explore the world and to flourish and survive. However, as articulated in phenomenological philosophy, the world is not the objective one of the natural sciences but it is the world as directly experienced in everyday life, and that is prior to scientific analyses and reflection. Human beings are part of this life-world, and they interact with it through perceptual activity. In this world, colors do not exist alone but always as colors of certain objects, operating within a visual field. Through colors, objects have meaning and significance, and that is why colors move us.

2.2 The Traditional View

In the Timaeus, Plato argues that colors are effluences emanating from bodies in the surrounding world. These bodies emit a stream of particles of fire that are perceived as colors. The color of a body is independent of the sentient beings which perceive it. Therefore colors are real and objective. In other works, however, Plato describes color as the private object of experience of the individual observer; it exists as long as a particular observer interacts with a particular object (Ierodiakonou 2005). Thus the status of color as a pharmakon is not clear: is it real and existing in the world or is it just how things in the world appear since, in fact, material objects have no color, as argued by Democritus and Lucretius, and color is merely a subjective experience? For a long time, these questions were not relevant. The received view on color until the seventeenth century was Aristotelian. It accepts that colors exist in the world, and that they reside in objects. If we see a red flower, it is red. According to Aristotle, colors are there even if they are not visible and if there are no sentient beings to perceive them. Light is required to make them actually perceived. Various colors are the result of the mixture of two basic colors, white and black (Ierodiakonou 2018).

2.3 The Scientific Revolution

Since the emergence of natural sciences in the seventeenth century, reality has been interpreted as quantitative, material and mechanistic. Qualitative properties of objects such as colors become problematic. They can only be incorporated into the scientific view of the world as constituted by physical components if they can be explained in terms of physics. The experiments of Isaac Newton in the 1660s were crucial for the physical interpretation of color.

Fig. 2.1 Isaac Newton’s prism experiment. Image created by Castellsferran (2020), Wikimedia, https://commons.wikimedia.org/wiki/
File:Experiment_dels_primes_d’Isaac_Newton_-_Refracci%C3%B3_de_la_llum.png
#/media/File:Experiment_dels_primes_d’Isaac_Newton_-_Refracci%C3%B3_de_la_llum.png, CC BY-SA 4.0.

Newton relates color to light, following the suggestion of Aristotle that light is the activator of color (Gage 1999). When visible light is refracted through a prism, it contains seven fundamental or spectral colors (red, orange, yellow, green, blue, indigo and violet). Each color has a specific length and frequency of electromagnetic waves. Red has the longest wavelength and violet the shortest. The surfaces of objects in the world absorb and reflect these waves so that specific colors become visible. The chemical constitution of materials determines what wavelengths are absorbed and reflected. If all wavelengths are reflected, we see white; if they are all absorbed, we see black. If the longest wavelengths are reflected, and the others absorbed, we see red. Newton’s studies have promoted physicalistic theories: colors are physical properties of material bodies and entities, and can be measured since they are written in the language of mathematics (Romano 2020, 66).

Fig. 2.2 Color wheel wavelengths. Image created by Amousey (2023), Wikimedia, https://commons.wikimedia.org/wiki/File:Color_wheel_vector.svg
#/media/File:Color_wheel_vector.svg, CC BY-SA 4.0.

2.4 Primary and Secondary Qualities

The view that color is not a property of things in the world also became popular among philosophers. René Descartes (1596–1650) compares color with pain. When we burn our hand in a fire, the pain is not in the flames nor in our hand but it exists in our mind; similarly it is an error to assume that colors exist outside us. Such error is the result of conditioning since early childhood because we have learned to associate sensations and perceptions with real things outside our mind (Descartes 1644). Colors are therefore problematic since they seduce and mislead us into thinking that they exist in the outside world. They do not really belong to the natural world, as described and explained by science. Colors are appearance, ideas within us, and not properties of things whereas physical properties of things are the cause of our perception of colors. In the history of philosophy, the status of color is defined by a classical distinction made by John Locke (1632–1704) between primary and secondary qualities. Colors are qualities and properties that require a subject, a substance; they cannot exist by themselves. According to Locke, qualities come in two types: primary qualities (such as bulk, number and motion of particles) which are essential and intrinsic; they define a substance. Secondary qualities are accidental or contingent; they are powers (or dispositions) to produce ideas in perceivers caused by the particular constitution of the primary qualities of the substance (Locke 1975). The temptation is to imagine that colors, as ideas in our mind produced by the primary quality of objects, are in fact in or attached to the objects themselves. Following Descartes, Locke repeats that this is a misunderstanding. Milk seems white but it is not; because of its specific constitution it has a power to produce in us the idea of white, but the color itself is not in the outside world.

2.5 Philosophies of Color

Color is the subject of numerous philosophical studies and debates, often in connection to the findings of contemporary science of color. It is not the aim of this chapter to analyze or summarize current philosophies of color but it will highlight several main issues which are important to understand the role, significance and use of color in healthcare and bioethics. Typical for many philosophies is that they elucidate the nature of color by localizing it either in the world or in the mind. In contrast to the traditional view they assume that there is a strict dualism between the subjective world of sensation and perception, and the objective world of physical facts (Chirimuuta 2015).

Realist theories, such as physicalism, identify colors with the physical causes of visual experiences of colors. They proceed on the basis of the commonsense view that colors are intrinsic, perceiver-independent properties of objects while they reconcile this view with scientific findings through interpreting colors as physical, and thus objective, properties (for example wavelengths of light) (Smart 1997). Doing so, it is not clear whether the nature of color as encountered in everyday life is indeed clarified. The question of color is answered with a physical definition, but it is a problem how light rays are able to cause sensations of color. Identifying colors with physical states has the effect that colors disappear from the world in which they are experienced, undergone and enjoyed (Thompson 1995, 32). There is often a clash between physical reality and perception of color. Depending on light, weather and context, colors are variable and seem to change whereas the physical causes remain the same. This also applies to the phenomenon of color constancy: perceived colors are relatively stable under changing spectral lighting conditions. Similar discrepancies occurred in Newton’s work. He identified seven spectral colors because he wanted to find a correspondence with the main tones in the musical scale. Visual experience, however, is different. Many people cannot differentiate indigo from blue (Eckstut and Echstut 2013). In the history of art, five colors have been regarded as primary (black, white, red, blue and yellow). This was based on pigments not light; only a few colors are needed to mix and produce other colors. In Newton’s system, black and white are not colors at all.

Other theories reject the idea that colors are objective properties of things. They advocate antirealism (Chirimuuta 2015): physical descriptions of the world do not refer to colors, and the appearance of color is therefore an illusion. Hardin (1993, 111), for example, concludes that “…we have no good reason to believe that there are colored objects.” These theories are often based on neurophysiological studies. They emphasize the importance of perception: wavelengths of visible light are only colors when we see them. Colors are just names or labels, and without perceiving subjects they are not there. They are produced and constructed in the visual system and do not exist outside of perception. The retina has two types of photosensitive cells: rods (to distinguish between dark and light) and cones (to distinguish among colors). There are three types of cones, sensitive to short, medium or long wavelengths, and usually labeled as blue, green or red. Light waves activate the rods and cones which then send messages to the visual cortex of the brain that interprets the physical sensation as the perception of colors, depending on what kind of cones are activated. Without cones wavelengths have no color. Neurophysiological theories thus provide an explanation of color in anatomical and physiological terms but they are subjective theories in the sense that color is not a property of objects in the outside world but completely perceived and produced within the perceiving subject. These theories reiterate Descartes’s view that colors are mental constructs, ideas within us, while we have the tendency to project them on external objects. The idea of projection is famously underlined by David Hume (1711–1776) who compares moral notions of good and evil, virtue and vice with colors (and sounds, heat and cold) which are not qualities in objects but perceptions of the mind (Hume 1978). They are projected on an achromatic world just like paint is used to cover and embellish objects. Arthur Schopenhauer (1788–1860), to name another philosopher, points out that colors are constituted through retinal and cerebral activities. He concludes that color is purely subjective (Schopenhauer 1994). But when colors are only situated in the eyes and central nervous system, they are in fact private mental states. How can we be sure that we see the same colors as our neighbors when there is no connection between wavelengths of light, coming from the outside world, and the neuronal activities within our brain that produce color, and no criteria to distinguish perception from illusion?

2.6 Color Relationism

One conclusion so far is that objective or realist as well as subjective or antirealist interpretations of color have the same effect: they assign a particular location to color; it is outside in the physical world or inside in our brains or mind (Romano 2020, 135). They reduce colors to either sensations and sense data that stimulate the human visual system or to perceptions that are constructed in the visual system itself. According to realism and antirealism, milk itself is not white. Because its molecular composition reflects all wavelengths of the visible light, our visual experience of milk is white. Since the wavelengths reflected by the milk activate the neuronal system, we have the perception of whiteness. In both cases the color does not exist in the outside world unless we take the physicalist view that identifies colors with wavelengths of light. We experience a significant discrepancy: the reality experienced through our eyes is colored whereas the reality according to physics and neurophysiology has no color (Chirimuuta 2015, 8).

To overcome the divergence of science and experience, it is helpful to critically examine some assumptions that underly the philosophical views of color. Chirimuuta (2015) mentions first of all the detection model of perception. Both realism and antirealism assume that through sensory perception true knowledge of the world is obtained. With the senses, physical properties of objects in the world can be detected. The eyes in particular are windows onto the world, comparable to physical measuring devices. The second assumption is reification of color. This is the idea that color can be abstracted not only from the context of the material world but also from other visual qualities such as size and shape. Color is indeed an entity or thing like dye or paint that covers an achromatic world, and that may be detected with perception. If it is real, the visual system will uncover it; if it is not real, it is the mind that paints the surrounding world. Color is therefore a quality independent from other secondary qualities that can be separated from primary qualities or rather the quantitative constituents of the world. The third assumption is that colors are located since there is a strict demarcation between the outside world of physics and the inside neuronal world of the mind or the brain. The consequence of these three assumptions is that color is not regarded as the interaction between perceiver and object. Together, these assumptions make it impossible to conclude, as Chirimuuta (2015, 17) underlines, that color vision is “a joint product of the perceiver and perceived, so colors are relational in this sense.”

Usually, colors are regarded as sensations or perceptions rather than as experiences which relate objective and subjective elements. Color perception is the detection of the chromatic properties of objects, separable from other visual aspects. Color is like an add-on that is dispensable without affecting the visual system. However, if color vision cannot be separated from the rest of vision, and is understood as interaction between perceiver and environment, colors do not simply belong to objects or observers. This idea of relation is expressed in the theory that colors are dispositions, for example in the work of Locke (1975, 135 ff). According to him, colors such as red or white are not in the objects themselves but their perception is produced by the powers or dispositions of substances. At the same time, these dispositions are the result of intrinsic qualities of substances, i.e. their atomic and molecular structure. Objects perceived as red or white have the disposition to produce the perception of these colors because of a physical infrastructure that absorbs and transmits certain wavelengths of light which reach the eye and are decoded in the central nervous system so that a color is perceived. Colors are real, but since they produce sensations they are subjective as ideas in the mind (the idea of redness or the idea of whiteness). They are therefore objective as well as subjective (Romano 2020, 40, 60 ff). However, precisely because of this duality, the notion of disposition is criticized. It is argued that dispositions do not cause their manifestations (Jackson and Pargetter 1997). For example, when a glass is dropped, the cause of its breaking is not its fragility but its internal constitution. Likewise, when an object looks red it is not because it has a particular disposition but rather because of a specific physical constitution, and then what really matters are physicalistic theories.

2.7 Ecological Theories

The view of color as a relational property is elaborated in ecological theories (Thompson 1995). Colors have a dual nature. They are Janus-faced, with one face turned to the world, and the other to the perceiving subject. The implication is that colors should not be interpreted as solely an intrinsic property of an object (determined by its physical characteristics) nor as an idea or mental construct (determined at neuronal level) but more appropriately as a relational property that brings together the object and its environment as well as the perceivers. Colors have a reality in the phenomenal world which is partly independent of human perceivers, and it is also more than a private mental state in the perceivers. This relational theory is influenced by an ecological view of colors that attributes specific functions to perception. The aim of perception is to identify certain characteristics of the environment that are useful for the survival of a species, to discriminate between beneficial and harmful objects, and to classify them. Non-mammals generally have a richer capacity for color vision than mammals. For example, many birds, particularly diurnal birds, have color vision in the near-ultraviolet region. This ultraviolet sensitivity is helpful to facilitate aerial navigation but also to recognize fruit trees and to identify ripe fruits among green vegetation. The same is true for forager bees; their sensitivity for ultraviolet light helps them to associate nectar or pollen with color patterns of flowers (Thompson 1995, 172). Color vision has various functions, for example perception of depth and distance, shape, contours, texture: “color perception is part and parcel of the mechanism for perceiving numerous different properties of objects…” (Chirimuuta 2015, 128). It is also necessary to identify objects (such as edible food); and furthermore has cognitive functions—for example, it helps to memorize objects and distinguish material differences between them. The emphasis is therefore on the usefulness of perception. Seeing with colors allows the perceiver to undertake activities; it is active interaction and engagement with the world, depending on the interests and needs of the perceiver. From an ecological perspective, color vision is primarily interaction with the outside world, not merely a matter of observation. It helps living beings to stay alive in their biological environments and to explore these environments (Romano 2020, 137). In the non-human world, seeing colors not only helps to detect objects against their backgrounds, but also guides interactions and behaviors because it serves to identify organisms belonging to the same species and to apprehend their sexual state. A recently studied example are desert locusts; when they live alone they are usually green or sand-colored to camouflage them against their background, but in large swarms adult males turn yellow. This color is a warning signal that prevents sexual harassment from other males (Cullen et al. 2022). In the animal kingdom yellow is often a color that adapts animals to their habitat (e.g. the giraffe and lion) but it can also be a sign of danger (e.g. yellow frogs that are poisonous).

Fig. 2.3 Yellow-banded poison dart frog. Photo by Holger Krisp (2013), Wikimedia, https://commons.wikimedia.org/wiki/
File:Bumblebee_Poison_Frog_Dendrobates_leucomelas.jpg
#/media/File:Bumblebee_Poison_Frog_Dendrobates_leucomelas.jpg, CC BY 3.0.

For human beings colors have similar functional roles, particularly within social and cultural contexts. Identifying colors has an instrumental value: “… it is rarely helpful to know the colour of a thing simply for its own sake: an interest in colour is typically serving some further end of the organism” (Campbell 2017, 185). Colors are used to distinguish and classify a specific social status, rank or profession. In Roman Antiquity, for example, red is the color of power and only preserved for specified officials such as generals and consuls. In many societies the use of color in clothing and food has been strictly regulated. Colors also have specific functions in religious contexts, such as referring to special days in Catholic liturgy. Monasterial orders have different colors for the habits of monks, while Buddhist monks wear orange. Colors are also used to diagnose diseases, and later, to determine microorganisms in the laboratory. Paints and pigments are applied to embellish the body with various types of make-up. On the basis of skin color, people are often classified and ranked.

2.8 Color Adverbialism

Dispositional and ecological theories consider visual experiences as revealing the nature of color in the outside world. Talking about color means pointing to the world around us. Both theories are relational since they attempt to bridge the gap between inner and outer, but Chirimuuta criticizes them because they connect the outerness of color with an ontological commitment that colors are properties instantiated by external objects (Chirimuuta 2015, 51). In her view they still regard color vision as the detection of mind-independent properties, and color as a property separable from other visual features. It is insufficiently expressed that colors are in between the physical and the mental, and that they are not locatable as inner or outer. It is necessary to go beyond the dualism of object and subject, and to avoid reification of color. According to Chirimuuta (2015) color vision is not first of all a way of seeing colors (with perception conceived as detection) but a way of seeing things (with perception conceived as discrimination). Colors are properties of specific kinds of events or processes, i.e. perceptual interactions. From this perspective, color is not situated in the world (realism), in the mind (antirealism), or in both simultaneously (relationism). Instead, color exists solely as a property of a perceptual process, and thus is better described adverbially rather than as a substantive. However, it is objected that in visual experience, as well as in the way colors are predicated in natural languages, colors qualify individuals rather than events. Colors are typically perceived as properties of things in a visual context (Thompson 1995). Color adverbialism would also counter-intuitively imply that without perceptual events (for example when there are no perceivers, or when they close their eyes) colors no longer remain in place (Cohen 2015).

2.9 The Phenomenological Perspective

The basic idea that humans are relational beings embedded in the surrounding world is crucial in the philosophy of phenomenology. It emphasizes that the analysis of phenomena like color should not start from the assumption of an objective world, and also not from a pure, constituting consciousness but from their unity and fusion. Being human means being-in-the-world, embodied being in a situation. It is impossible to separate the living organism from the world with which it interacts, but equally impossible to detach the surrounding world from the organism. However, this world is not the objective, physical or biological world of the natural sciences but the world encountered in everyday life and revealed in immediate, lived experience (Spurling 1977). In the immediacy of the experience there is no distance between humans and world; being human is fused with the world. We are, live and act in the life-world (le monde vécu) before we make this world the object of scientific reflection and analysis. The cognitive relationship between knowing subject and known object is preceded by the intertwining of human beings and world, and is first of all a perceptive relationship. Perception takes place at a pre-reflective level; it brings us into contact with the world that is prior to scientific knowledge; it is according to Maurice Merleau-Ponty (1908–1961), in contrast to knowing, a living communication with the world that makes it present to us as the familiar place of our life (Merleau-Ponty 1945, 64–65).

Perception is an activity or process that connects perceivers to their environments, as is also pointed out in other relational theories of color. For Merleau-Ponty, perception is not purely physiological nor psychological or reflective but a pre-reflective and pre-conscious interaction with the life-world. This materializes because we are embodied beings; our body is the only viewpoint on the world that we have. The body is situated in and part of the world and, at the same time, open to it. It is the body that actively organizes and patterns the visual field, depending on the tasks and interests of the organism, and determining possible areas of activity. Perception therefore is a bodily event, preceding reflecting and analyzing consciousness. The world is presented to me through my body.

Perception furthermore refers to context; for example, how and whether colors are perceived depends on the level and degree of lighting. We also do not perceive discrete, isolated objects but they are always linked to and surrounded by others, part of a ‘field’ and presented within a horizon. Colors are never simply colors; they are colors of specific objects. The blue of a carpet is not the same as the blue of wool. Colors form a system, embedded in objects and interwoven with other sensory data within a visual or phenomenal field. It is not possible to describe a color without referring to the object it belongs to—whether a carpet or woolen clothing—which feels and smells different, has a different weight, and responds uniquely to sound. The significance of perceived objects is immediately grasped in perception. According to Merleau-Ponty, a color is felt and the body responds before we are even aware that we see it. Colors have signification motrice: they touch and move us (Merleau-Ponty 1945, 243 ff). Red may exaggerate my reactions without me noticing, while green is restful. Colors bring about certain attitudes of the body and a particular way of perceiving, but this should not be construed as the effect of a specific quality upon an observing subject but as a pre-personal experience in the visual or phenomenal field. This field is meaningfully structured by the phenomenal body which is oriented towards projects and intentions calling for activities in the world. Phenomena of color are not in our minds or brains but they are how things present themselves to us in the life-world. They are immediately apprehended as meaningful and charged with significance. Since perception is communication or communion, they have the power to move us: “Quality, light, colour, depth, which are there before us, are there only because they awaken an echo in our body and the body welcomes them” (Merleau-Ponty 1964, 164).

2.10 Conclusion

In this chapter various philosophies of color have been discussed. It is common to distinguish between realist theories that posit that colors are objective properties of things, and antirealist theories that consider colors as ideas in the mind or mental constructs. Both types of theories are strongly influenced by scientific findings, particularly in physics, optics and neurophysiology. Consequently, philosophical theories often share the same assumptions as scientific theories. Colors are regarded as qualitative properties that have no proper place in the scientific image of the world as constituted by material and quantitative components; they are either physical or non-physical phenomena. They must be located in the outside world or inside the mind or the brain. But in both cases, color as experienced in everyday life disappears: as an objective, perceiver-independent property it is the effect of the physical state of things, and as a subjective, perceiver-dependent property it is produced by the visual system and erroneously projected on external objects. What the eyes perceive as colored has no color in the reality of natural sciences. Perception in these theories is detection and recording of objects in the outside world.

Color and its perception is understood differently in a third type of philosophical theories that emphasize color vision as the interaction between environment and perceiver. These relationist theories assume that color cannot be separated from other visual aspects of objects (such as form and matter). They also point out that perception is not merely detection but has a range of functions, specifically discriminatory and cognitive ones. From an evolutionary and ecological perspective color vision helps organisms to explore their environment, and to structure it according to what is relevant and helpful for their existence and survival.

Color as a relational experience is most clearly articulated in phenomenological philosophy. It stresses that perception is action, a process of connecting perceivers with their environment in order to guide behavior. Colors therefore cannot be located inside or outside the organism. Perceiving is an act not of the brain but of the organism; it is “a particular sort of activity in which the subject engages…” (Thompson 1995, 298). Furthermore, it is an embodied activity. The embodied organism is the subject of perceptual experience. The life-world of the organism is structured and patterned into relevant visual fields through the body. This highlights the importance of meaning. Color is best understood, in the words of Chirimuuta as “a means by which organisms make sense of the complexity of the natural environment” (Chirimuuta 2015, 15). Finally, relationism in general, and phenomenology in particular, emphasize the importance of context and life-world. As the world is not simply the physical, mechanistic and material world of the natural sciences, independent of the organism, it is impossible to separate the organism from the surroundings which with it interacts. At the same time, the organism is not a passive spectator that receives sensations from physical impressions but should be regarded as an active and exploring being making sense of its environment. In the life-world, colors do not exist on their own as abstract entities but they are always colors of certain objects and are operating within a visual field. In perceptual activity they highlight certain aspects of this field because they point to their significance and meaning. According to this philosophical perspective, seeing colors is not a neutral observation but has the power to touch and move us. This power will be the subject of the following chapter.

References

Chirimuuta, M. 2015. Outside color. Perceptual science and the puzzle of color in philosophy. Cambridge, MA and London: The MIT Press, https://doi.org/10.7551/mitpress/9780262029087.001.0001

Cohen, J. 2015. Outside color: Perceptual science and the puzzle of color in philosophy [review]. Notre Dame Philosophical Reviews, 21 October, https://ndpr.nd.edu/reviews/outside-color-perceptual-science-and-the-puzzle-of-color-in-philosophy

Cullen, D. A., Sword, G. A., Rosenthal, G. G. et al. 2022. Sexual repurposing of juvenile aposematism in locusts. Proceedings of the National Academy of Sciences of the United States of America 119 (34): e2200759119, https://doi.org/10.1073/pnas.2200759119

Descartes, R. 1644. Principia philosophiae. Amsterdam: Ludovicum Elzevirium.

Eckstut, J., and Eckstut, A. 2013. The secret language of color. New York: Black Dog & Leventhal Publishers.

Gage, J. 1999. Colour and meaning. Art, science and symbolism. London: Thames & Hudson.

Hardin, C. L. 1993. Color for philosophers. Unweaving the rainbow. Indianapolis, IN: Hackett Publishing Company (2nd edition).

Hume, D. 1978. A treatise of human nature. Edited by L. A. Selby-Bigge and revised by P. H. Nidditch. Oxford: Clarendon Press (2nd edition, original 1739).

Ierodiakonou K. 2005. Plato’s theory on colors in the Timaeus. Rhizai. A Journal for Ancient Philosophy and Science 2: 219–233.

Ierodiakonou, K. 2018. Aristotle and Alexander of Aphrodisias on colour. In: B. Byden and F. Radovic (eds), The Parva naturalia in Greek, Arabic and Latin Aristotelianism, Studies in the History of Philosophy of Mind 17. Cham: Springer, 77–90, https://doi.org/10.1007/978-3-319-26904-7_4

Jackson, F. and Pargetter, R. 1997. An objectivist’s guide to subjectivism about color. In: Byrne, A., and Hilbert, D. R. (eds), Readings on color. Volume I: The philosophy of color. Cambridge, MA and London: The MIT Press, 67–79.

Locke, J. 1975. An essay concerning human understanding. Edited by P. H. Nidditch. Oxford: Oxford University Press (original 1690).

Merleau-Ponty, M. 1945. Phénoménologie de la perception. [Phenomenology of perception] Paris: Gallimard.

Merleau-Ponty, M. 1964. The primacy of perception: And other essays on phenomenological psychology, the philosophy of art, history, and politics. Evanston, IL: Northwestern University Press.

Pastoureau, M. 2019. Yellow. The history of a color. Princeton, NJ and Oxford: Princeton University Press.

Romano, C. 2020. De la couleur. [About color] Paris: Gallimard.

Schopenhauer, A. 1994. On vision and colours. Edited by D. E. Cartwright and translated by E. F. J. Payne. London: Bloomsbury Publishers (original 1816).

Smart, J. J. C. 1997. On some criticisms of a physicalist theory of colors. In: Byrne, A., and Hilbert, D. R. (eds), Readings on color. Volume I: The philosophy of color. Cambridge, MA and London: The MIT Press, 1–10.

Spurling, L. 1977. Phenomenology and the social world. London: Routledge & Kegan Paul.

St Clair, K. 2016. The secret lives of color. London: Penguin.

Thompson, E. 1995. Colour vision. A study in cognitive science and the philosophy of perception. London and New York: Routledge.