[rojobuffalo]

Ya, that's a lovely comic, but it appears to be a misconception. That comic is actually specifically called out in the book on page 107.

It's more like a 12 color lookup table.

> Every kind of red stimulates the bottom receptor of row 3. All shades of violet stimulate the top receptor on row 1

That's based on an experiment where they were trained to attack colored lights for a reward.

The comic also says they have 16 color receptors, but the other 4 (2 in the midband and 2 in the hemispheres), as far as anyone knows, aren't involved in color vision.

[GoldenRacer]

Would they be able to distinguish between a light that is pure orange (a single 600nm wave length) and a light that is a mix of red and yellow that gives humans the perception of orange?

If so, I think that's still kind of a cool thing to think about.

[shrx]

It is my understanding that a mix of red and yellow frequencies would trigger the corresponding yellow and red-sensitive receptors, if it has them, but not orange.

[rojobuffalo]

That's my impression as well.

It's an interesting question. If you want to read more, the two researchers quoted in the book that I was summarizing are Justin Marshal and Mike Land. Each has a handful of papers that are cited in the bibliography.