In the history of discussions about consciousness, there have always been ideas that some aspects of human experience are irreducible to physics. Colors have long had a special place in these discussions. During the scientific revolution, colors lost their status as objective properties in the world, with people like Galileo relegating them to secondary qualities dependent on the observer, similar to taste, odor, or heat.
It didn’t take long for people like John Locke to begin wondering, does this mean that my red might be different from yours? Maybe when I see a red apple, my experience is what you have when you see green things, and your experience of the red of the apple is my green. We never notice the difference because we both look at the apple and call it “red”. In other words, we could have a difference in conscious perception of color that leads to no difference in behavior.
This has long been seen as a challenge for functionalism, the idea that mental states are about their causal role. If such a scenario is possible, the argument goes, then it seems to indicate that there’s something to color beyond the functionality, and possibly beyond physics.
Is there any necessity to red things looking red, or green things green? What exactly is red anyway? Or yellow, green, or blue? In short, what, if anything, is the function of color?
I think when pondering this, it helps to back up and think about the causal chain that leads to color perception, and then the downstream causal effects that result.
On the upstream side, the surfaces of objects absorb some wavelengths of light while reflecting others. When that reflected light enters our eyes, it excites photoreceptor cells, light cones, that are sensitive to that wavelength. The pattern of excitations results in patterns of nerve spikes being transmitted to the brain, which interprets that pattern as a particular color. Colors commonly map to specific wavelengths.
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At this point, it might be tempting to wonder if Galileo was wrong. Couldn’t we regard the reflective properties of surfaces as objective colors in the world? The problem is that this doesn’t map the same for all observers. For example, most humans are trichromats, with three types of photoreceptor light cones, enabling the most common color mappings. But some people are color blind, able to perceive few colors, often being dichromats, only having two types of light cones. And while primates are typically trichromats, most mammals are dichromats. Many other animals are tetrachromats, having four types of cones. Some have much more.
(Interestingly, a bull in a bullfight doesn’t charge at the matador’s cape because it’s red, but because the matador is moving it around. The red color seems to be for the audience’s benefit. Similarly, a lot of artificial coloring in pet foods are more for the benefit of pet owners than the pets themselves.)
And that’s before getting into other things that can affect color perception, such as adjacent colors, assumptions about lighting conditions, and a whole host of other factors. The infamous dress incident a few years ago highlights many of these issues.
All of which seems to indicate that color is a reaction of the observer to stimuli. The question is, a reaction in service of what? And that leads us to the downstream effects. Here things are less certain and more controversial. What we can say is that color seems to enhance visual discrimination, adding to the capabilities provided by shape distinctions and brightness levels.
On top of that, it seems like specific colors have higher saliency than others, indicating that they help in prioritizing attention. Assuming equal brightness levels and the absence of other shape triggers, red jumps out to us more than other colors. Yellow does too but to a lesser extent. They seem to say, “Look here”. It’s not an accident that most stoplights, error signals, and other high priority messages tend to be red. It’s also not an accident that many construction workers often wear yellow. By contrast, green seems more soothing, and blue even more so.
All of this makes sense when we consider the evolutionary background of primates, where high calorie fruits tend to be reddish and yellow, with green often being more backgroundish, and blue usually indicating the sky, so very backgroundish.
Individual colors also trigger particular emotions. As a recent study indicates, some of these are learned, but many seem to be innate. And individual colors have a wide range of other associations.
So what does all that mean for color inversion scenarios? As Alex Byrnes indicates in his SEP article on inverted qualia, switching around colors without affecting behavior runs into a number of complications. There are relationships between colors, brightness, and saturation levels that get in the way. So simply switching individual colors at random won’t work. We might try rotating the standard color wheel by 180 degrees, which preserves many of these relationships.
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However, as Byrnes points out, this changes how distinct the colors are for common foreground objects, at least in normal human vision, which seems to mess with one of the functions identified above, enhancing visual discrimination. And it all seems to be without bringing salience and emotional reactions into the discussion. Once that’s done, it’s hard to imagine an inversion not involving a change in behavior.
Of course, someone could insist that we just need to rewire all the associations so that we have the same reactions to shades of blue and violet that we previously had to reds and yellows. But here’s where the conversation gets metaphysical. Can we do that without effectively turning those colors into their inverts? If we give a shade of blue all the reactions we have to red, haven’t we effectively made it red? (In comparison, what if we changed the effects of a bitter taste to match those of sweetness? Would it still make sense to call it “bitter”?)
To say the colors don’t change here is to assert that there remains an intrinsic nature to the color independent of all its causal effects. I understand why this stance feels intuitive. But at this point it seems like we’re really talking about something ineffable and epiphenomenal. And when pondering the nature of a color, we have to remember that we’ve already identified distinctiveness, saliency, and other associational triggering as functional attributes. Maybe something is indescribable and epiphenomenal because it isn’t there.
Or maybe I’m missing something. What do you think? Are there aspects of color not captured in this discussion? If they’re ineffable, is there any way for us to establish their actual existence?
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https://selfawarepatterns.com/2023/03/05/the-function-of-color/
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