system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can a 4th primary color exist?

In one of the billions of universes that exist and stretch possibily to infinitiy, can a 4th color exist? Or is our color wheel a scientific fact of some sort that spans all of existence?
gpt
Humans are Trichomic, which is a fancy way to say that we see three primary colors.  This is because we have three types of color-sensitive cone cells in the eye- one red, one green, and one blue.  There is no way for us to see or perceive another primary color because it would require another type of cone cell to be present in our eyes.

There are many animals that have a different number types of cone cells in their eyes.  This allows them to see different primary colors than us.  Dogs for example are Dichromic (2 colors), and birds are Tetrochromic (4 colors). Some species have even have more cone types than that.

Fun fact: Goldfish are tetrochromic.  They can see red, green, blue, and ultraviolet as their primary colors.  Exactly how this is any use to them is unknown to me.