White light can be blinding, cold, unforgiving. Our physical reality often finds it too much as well, splitting it apart any chance it gets. Plants are green because such wavelengths of light help it keep a consistent vacuum on the electromagnetic energy it slurps from the sun. The sky is blue because of atmospheric particles that scatter light in slower wavelengths. The skin of an apple, a cherry, a tomato: all different ways of twisting light into hues of red. But despite attempts from the best scientists and philosophers, what color truly is, if it’s even anything tangible, remains elusive.

When it comes to the vexing problem of red or any other gradient, when we both agree that a thing is some color, is it really exactly the same as the color in your mind? Put another way, we might ask: is color even real?

Democritus believed that light refracting through atoms caused the phenomenon that we perceive and describe conventionally, or by mutual agreement, as color. By contrast, Aristotle believed that color inhered in objects. Throughout the scientific revolutions of the 17th Century, color was dismissed, along with other aesthetic properties like scent, as a secondary quality — that is, one lacking the explanatory role in the behavior of physical objects of so-called primary qualities, like motion or size or shape. Color was a frill, and perhaps an illusion. David Hume, the 18th Century philosopher, described it as “the phantasm of the senses.”

How color works

Unsurprising to some people, but most of what we learn in primary school about color is wrong.

We are taught the rainbow is composed of red, orange, yellow, green, blue and violet, and sometimes that there are invisible colors, infrared and ultraviolet, on either side. And we learn that there are three primary colors  —  red, yellow and blue  —  from which all other colors can be mixed. We play with them, as paints or Playdoh, and observe some rather muddy mixing. That’s because it’s not true that you can mix every color you can perceive —  the very act of mixing reduces a component color’s chroma, or degree of vividness, which is an essential part of that particular color.

We might be told that color has something to do with light, or even be shown a prism, through which light refracts to produce a rainbow. This is true, but the human brain and visual system can perceive more colors than are found in a spectrum or rainbow. We might learn that black is not technically a color, and that white is all the colors combined. But actually, black is a color, as well as white  —  they are achromatic colors, meaning those lacking  chroma (a level of vividness or mutedness, similar to saturation) and hue (the general family a color belongs such as green or yellow.)

In high school, we go on to learn that images are produced by the action of light bouncing off an object and interacting with our visual systems: our eyes, our brains, and the nerves and chemical messengers that connect them. It’s all very physical, very real. According to the Colour Literacy Project, from which Salon learned to bust all of the above color myths, what we learn about color is mostly wrong.

In fact, our visual systems are able to work on light from just one small part of the electromagnetic spectrum  —  the part ranging from violet light, which moves in quick, short wavelengths, over to red, with its slower, lower frequency, longer wavelength. Other creatures have visual systems that are responsive to different frequencies of light, with birds and butterflies able to perceive wavelengths in the ultraviolet range.

Flowers are of course well-known for their range of color, but have actually evolved entire palettes of color that humans can’t perceive. A daisy tinged with ultraviolet petals signals to a bumblebee: dinner’s served. But to us, it can appear as just a dull white or yellow. So clearly some colors “exist” in a way that we can’t totally wrap our minds around. 

Ultraviolet induced visible fluorescence, the natural fluorescence of flowers (Jose David Ruiz Barba / Getty Images)

On the other end of the spectrum is infrared, which is just beyond red and represents about half the light that reaches Earth from the Sun. It is visible to pit vipers as heat, giving them a Predator-like advantage for hunting. But even some humans can perceive infrared, and when exposed to longer wavelength infrared light in particular ways, may perceive a pale green or slightly redder color. 

It’s all in the mind

As we know now, colors aren’t just in the eye of the beholder, but it’s the brain that does the work, interpreting the information that the body gathers. Color occurs because our eyes are equipped with rods and cones — specialized light-absorbing cells in the retina at the back of the eye. The three different types of cones in our eyes each absorb different wavelengths of light. When light enters our eye through the pupil and hits the retina, our visual system compares the amount of light absorbed by each of the three types of cone. That information allows our brain to decide what color we think we’re seeing. In low light levels, only rods are able to absorb light, giving us grayscale vision. But if there’s a little bit more ambient lighting, colors look washed out, or low in chroma.

Humans have three types of cones but some animals have just two, giving them dichromatic vision  —  a more limited range of distinguishable colors  —  and others have tetrachromatic vision, with four types of cones conferring the ability to distinguish a greater range of color than us trichromats. It’s possible, though not confirmed, that some women have tetrachromatic vision  —  a 2010 study found that some 12 % of human females carry an X-chromosome linked color deficiency that gives them four rather than three types of cone  —  but that, at least for the most part, they don’t have a corresponding ability to see “four-dimensional color,” as the study puts it, perhaps because the type of cone isn’t the only factor in how many colors you can actually see. 

There’s also a lot of variation in what we each think we see when we look at, say, a red wheelbarrow. As authors Kara Emery and Michael Webster put it in their 2020 study of individual differences in color perception puts it, “individual differences are the standard, [and] an average function characterizes the behavior of few if any actual observers.” Variation in color perception is the rule, not the exception, for reasons that have to do with natural variation in the sensory mechanisms that allow us to take in a color stimulus, and in the mental processes that interpret it. After all, we’re not walking mass spectrometers.

“We don’t have equipment that sophisticated in our little heads, right?” Dr. Mohan Matthen, a philosopher at the University of Toronto, told Salon in a video interview. “But what we have is something that sort of gives you an approximation to that in a weird kind of way.”

So if you ask two people to identify, from a Pantone chart of greens, one square that contains no trace of blue and no trace of yellow, they will likely each pick a different green square. And yet we are at least able to both look at a green leaf and agree that it’s green  —  even though we have little reason to be confident that we’re having precisely the same internal experience of green when we do so.

But why would we evolve to have such variation in our color recognition? Well, new research from the Massachusetts Institute for Technology (MIT) suggests there’s a surprising advantage to this lack of precision, which relates to our developing eyesight. As infants, we actually start seeing the scenes around us in grayscale. This makes us more resilient to chromatic shifts later on, so for example we’re able to reconcile the subtle differences in color between a person in real life and the colors in their photo on our screen so as to still recognize them.

---

Want more health and science stories in your inbox? Subscribe to Salon's weekly newsletter Lab Notes.

---

Children who are born blind and acquire sight later in life  —  and therefore see in color from the start  —  are less resilient to such changes, the MIT study shows, suggesting they are more dependent upon color, and that the developmental process that begins with tones of gray and black and white contributes greater perceptive flexibility.

Additionally, research from last year has overturned the prevailing understanding of how the eye perceives color differences  —  an understanding suggested by mathematician Bernhard Riemann and developed by physicist and doctor Hermann von Helmholtz and physicist Erwin Schrödinger, all giants in their respective fields. As it turns out, using their geometry gives an overly large estimate of the human perception of differences between colors. That is to say that that model isn’t able to account for the fact that people perceive a smaller color difference between two widely separated shades than you get by adding up the small differences in color between them. We don’t yet have a new concept to replace this one, though.

Color factions

There are competing factions on the question of what a color actually is  —  or if it’s anything more than a figment of our imagination.

“It is reality-based, if you like,” Matthen told Salon. Colors “have some basis in the world.”

Matthen takes what he informally calls the “standard” view of color. It’s not as distant from reality as, say, the phenomenon of pleasure, which is far more dependent on our inner states than on the world: “If I find this cup of coffee pleasurable, that’s not a quality that’s in coffee — that’s just me reacting to it.” 

By contrast, Matthen sees color as more reality-dependent than the feeling of pleasure, while still being less real world-based than a so-called primary quality, like the movement or size of atoms. Secondary qualities are thus intermediate cases, with some basis in the real world: “Colour and also temperature, hot and cold flavor, certain kinds of characterizations of sound, high-pitched and low-pitched in sound, there are a number of these,” Matthen said.

The extremes on either side of this view of color are realism and idealism. In color realism, objects are thought to just have color, an internal attribute that is still there if you leave the room, or turn out the lights. This seems like common sense  —  but the scientific understanding we have today doesn’t support this idea. By contrast, to idealists, such as the so-called color fictionalists, everything is unreal  —  including color. Under that way of thinking, color might be considered a sort of consistent hallucination we have.

But as we’ve seen, between one person and the next, we are rarely perfectly consistent with color. The best we can say is that we generally mean roughly the same thing, give or take a few wavelengths, when we talk about a given color. So if we’re hallucinating, we may not be hallucinating exactly the same thing.

Color literacy

“By convention, we speak about color, about touch and sound, as if those things are in the world, but in reality, there’s just atoms in the void,” Stephen Westland, a professor of Colour Science at the University of Leeds in the U.K., and a member of the CLP, told Salon in a video interview. “However, I completely believe that color exists. So some people might think that either color exists out there in the world or color doesn’t exist. I don’t believe either of those things, but I think the majority of color scientists don’t believe either of those things either.”

There are other ways in which we might say color isn’t real  —  or that it’s more real than we think, depending on how you think about culture. That is, our cultural formation determines to a significant extent what colors we perceive and what we are incapable of seeing because our brains have not been taught to expect it. And while light is vital to our experience of color, what are we to make of our ability to remember in color, or to see color in dreams?

“I believe that color is a perception. It’s something we experience,” Westland told Salon. “But the reason I say that it’s ridiculous to say that it doesn’t exist, [is that] it’d be like saying that just because they don’t exist in the outside world, independently of us, there’s no pain or love. [It would be like saying] pain doesn’t exists, love doesn’t exist. Of course they exist … but they are constructs of our mental experience… If you removed all living creatures from the universe, there would be no pain. If you removed all living creatures from the universe, there would be no love, but there would also be no color, no sound, no taste, no smell.”

Westland said that in fact, it’s possible that what he experiences when he sees long wavelength light is what another person experiences when seeing short wavelength light. “This is called the inverted spectrum. Instead of me seeing it as blue at one end or red at the other end, you see red at the first end and blue at the other end. But we could have been taught from when we’re very young, we give it the label, whenever you experience that, you call it red.”

Thankfully, concepts that seem to be consistent, similar and universal like the idea of warm and cool colors or the emotional associations with different colors supports the idea that our experiences of color are at least fairly similar.

Still, stare too deep at the idea of the inverted spectrum and you may end up unsure about everything. 

Never mind color — nothing is real

“That’s actually quite a terrifying thought,” Westland said of the inverted spectrum, “because this is not just about color, remember, it’s about everything. It suggests that one possible explanation is each of us is living a reality that would be alien to the other person … and it could well be that what I experience when I see a long wavelength light is what you experience when you hear a bell ringing.”

In fact, the question of color posed in the question beloved of clever eight-year-olds  —  “is my red the same as your red”   —  is about far more than just color. It’s really a question about consciousness and reality. Philosopher Thomas Nagel, in a famous 1974 essay on subjectivity, “What Is It Like to Be a Bat?” puts it like this when he imagines how one might try to explain sight to someone blind from birth:

“The loose intermodal analogies — for example, ‘Red is like the sound of a trumpet’ — which crop up in discussions of this subject are of little use. That should be clear to anyone who has both heard a trumpet and seen red.”

Being sure that two people seeing what they each call ‘red’ have the same experience when they of it, Nagel effectively argues, is ultimately as impossible as it would be for us to know what it is like to be a bat, having an entire sensory apparatus we lack. That is to say: you can explain in incredible detail what it’s like for you, you can use metaphors to help me imagine my way into your experience, but the experience itself remains ultimately subjective.

I can know what it’s like for me to see a red wheelbarrow, as in William Carlos Williams’ famous poem in which, “so much depends/upon//a red wheel/barrow//glazed with rain/water//beside the white/chickens.” But there’s no reliable way to know what it’s like for you to see the same wheelbarrow, upon which so much depends. Thinking like this can turn you into a color skeptic.

It gets even worse than that, though. As Emery and Webster note in their 2020 paper, even our own visual reality can change dramatically over time through normal development, disease or aging, and according to whether we’re looking at something in the center of our gaze or in our peripheral vision. These variations within our own reality can be as great as the variation between individuals: “[I]t is important to emphasize that this physiological variation can be equally dramatic within the individual, across both time and space …Thus even an individual observer “sees” the world through a visual system that is very different at different times and locations,” the researchers write.

This way lies madness.

If you stare too hard at a color while wondering if every one of us is living in our own completely distinct reality — or if there are completely distinct realities living within every one of us! — well may you hear those alarm bells ring.