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Is there any objective, scientific way to prove that we all see colours the same? I know it's one thing for two people to point at an object and agree on its colour, even the particular shade, but there's no way that I can tell whether or not the next person in line sees everything in shades of greys, or in negative. We can even study how light interacts with objects and enters our eyes, without truly knowing if one person would see everything the same if he suddenly were able to see though another's eyes. So, is there any proof that we all do see colours the same? Maybe even proof or evidence to the contrary? If that's so, I must say that you're all missing something great from where I can see.

This is a much discussed question, which often appears in the guise of the " inverted spectrum hypothesis ": One might wonder whether some other person sees what you see as red the way you see green, etc. It turns out it can't be quite that simple, but one might nonetheless wonder whether we do all see colors the same way. In fact, Ned Block has argued that there is some empirical evidence that we don't all see colors the same way. (See this paper .) It goes without saying that this is very controversial.

Can a new color be made that is not like, or mixed from, any other?

The answer to this question obviously depends upon what color is. and I haven't a clue. But there is a little we can say anyway. Let us ask: Could there be a color that human beings perceived that was utterly unlike any other? To this question, I think the answer is no. Human color perception, it is now pretty well-established, is tri-chromatic, which means that color-space, as humans perceive it, is three-dimensional, the three dimensions characterized by the primary colors. I suppose it is possible that there are some colors no one has ever perceived that would appear utterly unlike colors to which they were nonetheless chromatically related, but human color vision also appears to satisfy some kind of continuity principle that would rule out that possibility. Some birds, it appears, have vision based upon four dimensions. If so, then the structure of color-space as they perceive it is radically unlike ours. Whether that means that there are colors they perceive that we do not, or whether it...