Improved tetrachromacy
Humans can already experienced a limited form of tetrachromacy in dim light via cones and rods working together but unfortunately at those dim lights the cones have rather limited functionality so overall color differentiation ends up being worse than at brighter light. The problem we need to solve to enable highly functional tetrachromacy is to find a way to make the rod receptors not get saturated to the point where they stop being useful for color differentiation at normal light levels.
In rare cases females have a forth cone type between green and red but it's unfortunately
not very helpful since there is no particularly good placement for it (due to the red and green already being quite close). As we see from the picture above the rods have a far better color frequency response for enabling highly functional tetrachromacy and all we need is to find some mutation or resort to genetic engineering to make them useful at high light intensities.
Rawaga wrote:
Rod-tetrachromacy is a thing, but it's very conditional. It only works in specific mesopic lighting conditions. However, whenever such lighting situations are active, cones are stimulated so little that the overall amount of colors you can see in this tetrachromatic system is a lot less than in daylight with normal trichromacy. On top of that, there are very few rods in your fovea (i.e. the center of your vision) while most of your cones are located in the fovea. The result of this is that any degree of rod-tetrachromacy is only experienced inside a ring shape around the center of your vision, which is always out of focus.
https://jov.arvojournals.org/article.aspx?articleid=2430812
Next, most people misunderstand how tetrachromacy increases color space and quantity. Since the rod response overlaps so much with the M and S cone response, and also considerably with the left tail of the L cone response, e.g. any green you see with this vision will always have "rhodon" (i.e. the rod color quality) mixed into it. Because of this substantial cone response overlap the amount of additional tetrachromatic colors you see is not as much as you'd expect, in addition to you not being able to see normal trichromatic colors normally. Furthermore, tetrachromacy doesn't make you a better trichromat, but rather extrudes the virtual color space into a 4th dimension of color.
It's still a tetrachromacy, of course, and awesome to experience. But you really have to look for how it changes your color vision and understand how tetrachromacy works to properly experience it. Qualitatively, if you're doing test for yourself in mesopic lighting conditions, you should look for how colors are now overlaid with a "cyanish haze", for example. It's not "cyanish", per se, but the rod color quality. But its quality is closest described as a "whitish-cyanish" overlaid on top of other colors.
