Why Can’t We Say What Color Our Skin Is?

Corey’s post about the more toxic stuff in Jefferson’s writings was interesting, wasn’t it?

This bit –

Are not the fine mixtures of red and white, the expressions of every passion by greater or less suffusions of colour in the one, preferable to that eternal monotony, which reigns in the countenances, that immoveable veil of black which covers all the emotions of the other race?

– reminded me of something else I read recently, in The Vision Revolution: How the Latest Research Overturns Everything We Thought We Knew About Human Vision , by Mark Changizi [Kindle version only $1.99. Good deal!]

The book manages to hit the popularized-but-substantive sweet spot pretty consistently. The chapter on skin color reports some of Changizi’s own research. He starts with a puzzle: why is it no one has a good name – a name they are satisfied with – for their own skin color? ‘White’ people aren’t white: tan, pink, salmon, off-white, peach? There are 11 ‘basic’ colors, per Berlin and Kay. None are good descriptors of anyone’s skin color. This result generalizes. ‘Black’ people aren’t any better at finding words for their own skin color they are satisfied with than ‘white’ people are.

Why would that be? A hypothesis.

Consider an object with a color that is highly categorizable—say an orange. If I place 100 oranges in front of you, there will actually be some variation in their colors, but you won’t pay much attention to these differences. You will subconsciously lump together all the different hues into the same category: “orange.” Ignoring differences is a central feature of categorization. To categorize is to stereotype. When a color is uncategorizable, however, the opposite of stereotyping occurs. Rather than lumping together all the different colors, you appreciate all the little differences. Because our skin color cannot be categorized, we are better able to see very minor deviations in skin color, and therefore register minor changes in others’ skin color as they occur. This made me wonder whether this is no accident. Could our color vision have evolved so for this precise purpose?

What would be the point?

Uncolorful, uncategorizable skin tones are just what we’d expect if color vision were intended for mind-reading through the window of skin.

This compresses a couple of thoughts, and is genuinely a surprising proposal; but first let me get back to the Thomas Jefferson point. The following passage from Changizi says the necessary:

If our skin color is so uncolored, why do we use color terms so often to refer to race? Races may not literally be white, black, brown, red, or yellow, but we wouldn’t use these terms if we didn’t perceive other races as having colored skin. So what is all this nonsense about skin being uncolored? One must remember that it is only one’s own skin that appears uncolored. I perceive my saliva as tasteless, but I might be able to taste yours. I don’t smell my nose, but I might be able to smell yours. Similarly, my own skin may appear uncolored to me, but as a consequence of using senses designed to perceive changes around a baseline, even fairly small deviations from that baseline are perceived as qualitatively colored, just as a slightly warmer temperature is perceived as hot. An alien coming to visit us would find it utterly perplexing that a white person perceives a black person’s skin to be so different from his own, and vice versa, when in fact, their spectra are practically identical (see Figure 3). But then again, this alien would also be surprised to learn that you perceive 100-degree skin as hot, even though 98.6 degrees and 100 degrees are practically the same. Therefore, the fact that languages tend to use color terms to refer to other races is not at all mysterious. It is consistent with what would be expected if our color vision was designed to see color changes around baseline skin color. Your baseline skin color appears uncategorizable and uncolored, whereas skin colors that deviate even a little from baseline appear categorizably colorful

Thus, skipping ahead a bit:

As a whole, these illusions lead to the false impression that other races are qualitatively very different from ourselves and that other races are homogeneous compared to our own. It is, then, no wonder that we humans have a tendency to stereotype other races: we suffer from perceptual illusions that encourage it.

No doubt that is also why, on Star Trek, all members of every race besides the human race seem to have the same haircut. Probably, to Vulcans, Spock’s smooth black bowl looks very different from some other Vulcan’s smooth, black bowl.

Getting back to mind-reading: Changizi’s original contribution to the field, I take it, is the idea that our capacity for color vision may actually have evolved to allow us to see the color of our own skin, even though we can’t say what color our skin is. The standard line on primate color vision has been, for a long time, that it evolved to help us find fruit (by making it pop out of the background, visually.) The problem with this hypothesis is that different sorts of primates have very different diets but they seem to have similar similar visual capacities. Different diets, same eyes. So maybe the eye is not calibrated to the diet.

With my skin hypothesis, on the other hand, there is no mystery as to why all primates have such similar color vision. Although skin colors vary across primates, we all have the same kind of blood. As we will see in the following section, no matter the primate, as blood changes in oxygenation and concentration, skin is spectrally modulated in the same ways. That’s why we primates have the same kind of color vision.

Skipping ahead:

Specifically, two features of blood matter here: (i) the quantity of blood in the skin, and (ii) the oxygenation level of that blood. As we will see later, our color vision is able to sense these blood qualities—but how do changes in these two features change the color of skin in the first place? If there is less blood under the skin than normal, skin appears yellowish. If there is more blood than usual, skin appears bluish. If the blood is more oxygenated than normal, skin appears reddish. If it is less oxygenated than usual, skin appears greenish.

Different emotional states, states of health and energy and distress and injury and so forth can be registered in the skin, then. (Changizi goes on at some length about this.)

What is the significance of skin’s color-changing ability? It is an indication that color vision is designed for seeing skin color changes. To understand why, ask yourself: How many other natural objects can dynamically achieve every hue and also appear to have no color? Fruit can go through several hues over the course of a week as it ripens, and leaves can also display multiple hues while maturing. But neither fruit nor leaves can hit every hue, much less do so in such a dynamic manner, able to pass back and forth between hues. The only other objects in the natural world able to display multiple hues are the skins of just a few other animals, such as the chameleon and the squid. One group of researchers led by biologist Ruth Byrne has classified the colors dynamically obtainable in a reef squid as “pale, white, yellow, gold, brown, and black.” Other cephalopods are able to appear blue, but only in metallic shades. The skins of these animals do not, however, appear able to display a continuum of hues, nor can they return to baseline or “turn off” like human skin, at least not to human eyes (e.g., squids at baseline appear gray, and chameleons at baseline appear green). An object capable of dynamically displaying all possible hues and also appearing uncolored is, then, a rarity in the natural world. And if you do find an object that is capable of reaching all the hues and also returning to a baseline, then it is very likely to be by design, whether human or evolutionary. It suggests that it is no accident that skin can display all the hues and has an “off” switch. Skin is a full-color monitor by design— design by natural selection.

Also, maybe that’s why we lost our fur. To ‘talk’ to each other through our skin. More specifically: to speak the truth to each other. The blood doesn’t lie. Important data point: primates that have furry faces (and bodies) lack color vision.

Doubling back to the race question: Changizi notes studies to the effect that doctors are better at diagnosis for patients of their own race (i.e. their own color baseline.) [UPDATE: I was misremembering. The cases concern color-blind doctors. Changizi speculates that the phenomeonon might generalize to doctors treating patients not of their own race] They notice subtle differences in skin tone relative to their own, accustomed baseline normal – a flush, a pallor – that they would miss if the patient looked to them ‘black’, or ‘white’, or ‘yellow’. A corollary, which Changizi doesn’t really discuss (although I’m sure he’s thought about it) is that there could be a deep, biological reason why differences in skin color (not difference in ‘race’) are ‘natural’ engines of xenophobia, ethnocentrism, all that good stuff. We can’t easily ‘read’ people whose baseline coloration is different from our own. We are used to getting a flow of data, without even being aware of where and how we are getting it and what it is. When the flow is not there, we probably blame the sender for cutting off the flow. Members of groups with a different color baseline seem emotionless, deceptive, shifty, or dull, or any number of other negative things.

If that’s how it is, it makes sense that people get more worked up, and driven apart, over skin color than they do about other possible characteristics that might be possible markers of ‘race’: height, weight, body type, hair color, nose shape, on and on. A standard point of racial harmony rhetoric is that color, being a superficial thing, is a silly thing to fixate on. But color that is a super-sophisticated full spectrum monitor and mind-reading device is a horse of a different color.

A final note: I’ve just written this post in a rather authoritative tone for simplicity. But I’m not personally an authority on the subject. Also, I don’t just take it for granted that, because it says so in Changizi’s book, his must be the final word on the subject. I’m aware that there is often dispute about these matters. Last but not least, I’m aware that just because these results are kind of nifty, if they stand up, it doesn’t follow that they are a grand unified explanation of the whys and wherefores of racism and ethnic strife and all that. It’s quite clear that this skin stuff is, at most, one factor among a great many factors.