More on Rainbows

In earlier post, I talked about the questionable nature of the "7 colors of the rainbows".   But I failed to talk about why the bands of colors are uneven, never mind how many there actually are.  In the picture below I have overlayed an enlarged picture of a real rainbow and a graph of the sensitivities of our three cones.  As you can see, the narrow sharpness of yellow and the wide blending of blue into violet and red into orange come from the ranges over which the individual cones are sensitive!

There is some evidence that a few women (need two X chromosomes for this theory to work) are born with four kind of cones (like most birds!) and can discriminate even more bands of colors that the rest of us.

Dogs, on the other hand, only have two types of cones and so are partially color blind.