Since the pre-Socratics, it’s been argued that unlike things like shape, color ‘is not out in the world’, but ‘inside our minds’. I am never quite sure why it is that shapes are ‘out there’, while colors are ‘in here’. In all cases, our sensory modalities transform a kind of energy into a subjective experience. Thus, either everything, from shape, to color (sound, smells, flavors, etc.) is in here, or everything is out there. It seems to me that the main incentive to argue that color is ‘in here’, is the fact that our experience of it as utterly subjective. The line of reasoning seems to be: There is no telling how you experience the color of that shirt, therefore color is in our mind. I was never comfortable with this inference. It seems to presuppose that color is exclusively the quality of our subjective experience, while the question at hand is precisely ‘What is the nature of color?’ Sure, I have a subjective experience of color. But why would I deduce from that, that there is nothing more to color than my experience of it?

There is no room in this post for me to go over this discussion, but there is one particular idea I would like to share. It pertains to a comparison of color to heat. The usual argument is that temperature and color are both subjective experiences, but unlike heat, color cannot be measured. As a result, philosophers are comfortable saying “This water is 28 degrees” but not “This object is blue”. They would rather say “This object appears blue to me under certain conditions, at a certain time”.
In a conventional way, we’ve attributed the different numbers of the thermometer to different magnitudes of energy, and I have learned that 28 degrees is a warm enough water to get into – while 19 degrees might be a little too cold. There is a one-to-one correspondence between the energies producing heat in the water, with the number displayed on the thermometer; and between the number displayed on the thermometer and my concept of the water’s temperature. Clearly, the thermometer does not measure my experience of temperature. But we do consider that it measures the temperature the water is. In the case of color, the argument goes, there is no such thing.

Take the colorimeter, a device that displays a certain number when exposed to a certain wavelength. I could learn, like in the case of the thermometer, that this number maps onto my concept of ‘blue’. Wouldn’t there be in this case a one-to-one correspondence between the wavelengths reflected by the object, and the number displayed, and between the number displayed, and my concept of blue? Yet, in this case, people are inclined to say that what this colorimeter measures are wavelengths, not color, even if they would grant that the thermometer measures temperature – not the energies that produce the sensation of heat in me.
A first objection I can think of to colorimeters, is the fact that they’re not intuitive. My experience of heat varies linearly, and therefore the range of increasing numbers found in thermometers seems to capture this essential aspect of temperature sensations. My color experience does not vary linearly, although the measured wavelengths do. There would seem to be a discrepancy between the two representations, that of the colorimeter, and that of human beings.
Metamerism is the second objection. Metamerism occurs when humans perceive two objects, which reflect light differently, as being of the same color. Thus, the colorimeter may offer one-to-one correspondence between the reflected wavelength and color concepts, however, there is no such correspondence in our experience of color. The colorimeter’s failure to capture metamerisms shows that it does not adequately characterize our experience of color. Again then, that our experience of it is color’s main defining feature is the ruling assumption. The presupposition seems to be that color is exclusively the visual sensory experience of a certain kind of information available in the world. That information however, is not taken to be color. But what if we could have a different kind of experience of that same information? What if we could touch, or hear that information. Wouldn’t we say that we have a tactile or auditory experience of color? Wouldn’t that imply that there is something out there that we can call color?

In a fascinating TEDex talk, Neil Harbisson, founder of the “Cyborg foundation”, presents the “eyeborg”. By birth, Neil cannot perceive colors and only sees the world in black, white, and shades of grey. The eyeborg is a device about the size of a quail egg, which hangs on top of Neil’s forehead. It is sensitive to wavelengths, and transforms this information as vibrations to Neil’s skull, to which it is permanently fixed. Neil perceives these vibrations as sounds. The sounds are set so that they correspond to 360 hues that humans can discriminate. With time, Neil fully adopts this ‘sonochromatic’ scale, and naturally associates certain notes to color concepts. Far from reproducing the visual color experience humans normally have, what Neil has nevertheless, is arguably an auditory experience of color. Even though Neil has never seen color before, he can identify through sound what we see as color; and what other species see as color, like infra-reds and ultra-violets. To Neil, the world he hears is colorful.
What this could be taken to suggest is that there is color information in the world, an information that allows us to distinguish objects more rapidly from their background, to distinguish edges and volumes more efficiently, independently of how we qualitatively experience it. That we can only see rainbows does not mean that they can only be seen. The fact that cyborgs can hear them should make us think that there might be color ‘out there’ after all.

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