What would happen to ones mind if they were to experience the sight of an
I don't think anything too spectacular would necessarily happen. One reason is that one might not even notice it when it happens. For example, at some point in history, we can imagine that no one had experienced the sight of the color of coca cola in a green glass being hit by a sunset in the Mediterranean at some specific angle, on a specific day of the year, at a specific time. We can imagine that this specific color cannot be achieved by any natural process, so that until this point in history, no one had experienced this color. However, the color is just barely noticeably different from lava seen through polarized 3-D sunglasses in Hawaii, in certain specific viewing conditions. And, we can imagine, the lava had been seen before in such a way. So, now: what happens to viewer, on a yacht in the Mediterranean, when she sees the coke? Nothing much, I think. She may make a note of the odd color, but why think that anything else would happen?
I think at some point in history, someone was the first to see neon colors (such as glowing neon pink). I think they must have thought it was cool, but I doubt anything truly mind-blowing happened. And neon hues probably should count as entirely new, since they really are distinct from other experienced colors. I might be wrong about that...that's a question for historians.
Now, you're thinking: this panelist has missed my point! I meant, what would happen if it is an ENTIRELY different sort of color, not just barely different from what anyone has happened to see before? I'm not sure I can imagine it (though I can imagine, if David Hume was right, a new shade of a familiar color that I have seen before). I suppose it would be a bit like a blind person seeing colors for the first time. I would, I suppose, thereby acquire new abilities to imagine things in the color. But, again, I don't see a reason to think anything much more than that would happen.