Richard Dawkins writing for richarddawkins.net:

A recurring conundrum in philosophy is the impossibility of sharing, or describing to a blind person, the subjective sensation of colour. Is my sensation of red the same as yours? Or do you see an entirely different hue that I cannot even dream of?

Do you see the number 15 here? People with color blindness cannot

It seems impossible for me to imagine a colour that I have never seen. I don’t mean some subtle shade in a paint catalogue, intermediate between colours that I know well. I mean a completely new colour, as different from the familiar as red is from blue. Proverbially we call it sky-blue-pink, but of course it would resemble no name-able colour.

I have long argued that subjective hues are constructions manufactured in the brain as convenient internal labels for light of different wavelengths. There is no reason why your brain should use the same label for red as my brain does, just because both are labelling light of the same wavelength. I have even gone so far as to speculate that bats might hear in colour. The bat’s brain constructs a detailed picture of the world using echoes instead of light. A bat, when echolocating an insect, might use the subjective sensation that we call ‘red’ as a convenient label for the furry texture of a moth, and might use ‘blue’ as an internal label for the leathery texture of a locust. These qualia are just conveniences, to be pressed into service in the way that is most useful for the species concerned. Since the mammalian brain has the capacity to construct the qualia that we call hues, and use them as internal labels to facilitate sensory distinctions, why wouldn’t bats, as fully paid-up mammals, press into sonar service the labels that we call red and blue? By the same token, I went on, perhaps rhinoceroses smell in colour.

But always, lurking in the background is the desire to imagine a completely strange and alien colour sensation, a colour never seen. I have no hope of ever enjoying that remarkable experience, not even on an LSD trip. But yesterday I nearly hit another cyclist who shot a red light and pleaded colour-blindness as his excuse, and immediately an intriguing thought occurred to me.

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