Pictured: BULLSHIT. (Not really. Image found at Quora.)
For one thing, some people are colorblind. But it gets so much cooler, and so today I'm writing about color perception!
You may have heard of the rods & cones in our eyes, and the short version is that rods help us detect brightness while cones help us detect color. Rods are older, evolutionarily speaking, and much more responsive insofar as they take fewer photons to activate. But cones, in helping us see color, allow us to distinguish predators among busy backgrounds and detect the ripeness of fruits.
Also found on Quora, but for a totally different conversation.
Interesting Miscellanies which You Prolly Know but Maybe Not
Most human beings are "trichromatic," having three kinds of cones: red, blue, and green. These respond, logically enough, to those corresponding colors of light. This means that the only reason the RGB breakdown works is because it corresponds to our machinery, not because that's how anything "really" is. But in some people, one of those sets of cones doesn't work, and they can't distinguish colors so well. And there is of course more to it than that, but most people know about colorblind folks and it gets way more interesting than this so we are rolling right along!
On the opposite end of the spectrum (so far) are tetrachromats, people who have four kinds of cones in their eyes and can see not 33% more colors (as one might expect), but many times more colors than us measly trichromats. This is because tetrachromacy doesn't "just" tack on another "kind" of color, but adds another dimension of color. So on top of all the R values that can be mixed with all the G and B values, there's a fourth set of values that can be mixed with all of the previous. But there's still more interesting to go!
The mantis shrimp sees our two to four color receptors, and raises: they've got twelve to sixteen color receptors, on top of each eye being trinocular and thus independently depth perceptive. Moreover, they can tune some of these receptors at will, and I don't even know how to imagine that twist on this thing I already can't imagine. The mantis shrimp's eyes are truly a thing to behold, and I really wanna know what it's like to have them, and The Oatmeal made an amazing comic about it so just go read. But even the mantis shrimp has to take a backseat to the very most interesting bit about color vision, and how we know sure as dammit that some people's red isn't the same as other people's red.
The Most Interesting Part of All!
Color perception is also influenced by culture. Yeah, yeah, talk about the wine-dark sea and hair being compared to blue stones in Ancient Greek literature all you want, but this is some present-day go out and check now science. Sadly, the video is now down, but it was explained in a BBC program and the episode was entitled "Do You See What I See?" (because of course it fucking was). So some scientists found a tribe called the Himba and investigated their color terms and then devised a test: show twelve swatches of color in a circle, eleven of which are identical, but one of which is different by a small but measurable RGB value. We'll circle back after a brief tangent.
Us Westerners, with our internet and fashion industry, have pretty regular color terms (among present-day Western cultures, that is); this leads us into the trap of thinking they're objectively real and universal. Our science of color perception has noted that cultures first develop terms for black and white, then red, then yellow (just like the TooL song), and so on; this leads us into the further trap of thinking that other cultures' color terms are deficient or primitive when they differ from ours. But it turns out that other cultures can have color terms just as nuanced as ours but still different. We can test this because we can make objectively different RGB values and then interrogate people for their subjective color distinctions. I don't mean like Randall Munroe's color survey where clearly different colors are given the same name, I mean when actually different colors are perceived by us as the same color.
Not this, in other words. But this:
(Top image from xkcd, bottom from PetaPixel's write-up of the documentary.)
Getting back to aforementioned test: the image on the right has one swatch that's slightly more blue than the others, and the image on the left has one swatch that's slightly more yellow than the others*. I bet you, being an Internet Person, are able to quickly & easily distinguish the odd one out on the right, but not on the left. However, the Himba people of Namibia are the reverse from us: they are able to distinguish the left set just as quickly & reliably as we can the right set, but they guess on the right set just as unreliably as we guess on the left set. This is because the Himba distinguish more greens/yellows than us, but we distinguish more greens/blues.
Go ahead and take another look at those circles above, if you haven't already checked out the note below. If you can't tell which one is different, SPOILER ALERT it's the same position in both circles. /SPOILER If you try real hard, you might be able to see the difference, now that you know - but would you really bother to single out that one square if asked whether they were all the same or if one was different? If someone told you that the squares on the right looked all the same to them, would you say OK or would you call them colorblind? In a way, this should be no more surprising than the fact that fashion industry professionals distinguish more colors in general than most of us (how many shades of grey do you really need, without a professional reason for training yourself to distinguish them?). But the fact that the Himba so easily distinguish the left circle while having such difficulty with the right tells us, for sure, that what we see as blue they see as green as the rest of the circles - and vice versa for the circle on the left.
Age-Old Philosophical Problem: solved! We don't all see the same colors, it's influenced by a lot of things, from biology to culture.
Notes:
* - SPOILERS IF YOU'RE TRYING TO SOLVE IT YOURSELF! I went & tested the RGB values, and it's a little disappointing because the "basic" green swatches are all 78/186/12, the blue one is 36/194/233, and the yellowish one (same position on the left) is 96/192/4. Calculating the differences between them, the blue one is considerably more different than the others are from each other. I went and made one that was "bluish" by the same numeric amounts as the yellowish one, and it didn't look very much different (and I also knew which one it was in advance, making the difference more noticeable to me). But I was also able to distinguish the yellowish one, because I looked at the one on the right and then on the left and thought it was in the same position, but then I thought maybe it was just an after-image, so I looked at the one on the right and then turned the screen and looked at the left one, and the same one (now in a different position) looked different, so I figured I was right. Then I tested them and I was vindicated, Hooray The End.
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