Hmm, but my understanding is that humans who are natural tetrachromats see more colors in the yellow-red part of the spectrum
There is genetic evidence that some people might be natural tetrachromats, though as far as I know only one case has been confirmed, sort of. If this is true these people would have an additional Q type cone cell, with responsivity in the visible spectrum (so they don’t see UV). The mean responsivity of Q cells is in between M and L cells with heavy overlaps, so many of these new color qualia are also inaccessible.
And humans already can see UV light a little, but the thing that stops this from being visible is actually the lens, which blocks UV light normally to protect our eyes
UV-A is not stopped by the lens and can reach the retina.
There is genetic evidence that some people might be natural tetrachromats, though as far as I know only one case has been confirmed, sort of. If this is true these people would have an additional Q type cone cell, with responsivity in the visible spectrum (so they don’t see UV). The mean responsivity of Q cells is in between M and L cells with heavy overlaps, so many of these new color qualia are also inaccessible.
I think it’d be more interesting to expand the frequencies that humans can see rather than just add a new color among the current visible spectrum. Many birds and flowers possess features with colors in the UV which we cannot appreciate right now. Also, squeezing more peaks inside the visible spectrum without expanding it might be difficult if we also want to keep these curves decetly separated.