Some animals have more cone types than humans, especially various birds, so would probably see a violet sky.

We don't have this because common ancestor for all mammals lost all cones but one, perhaps due to being nocturnal, and a second was re-evolved as mammals became more dominant (after dinosaur extension). A third cone was evolved in primates due to a gene duplication that gave us our green cone

https://www.sciencedirect.com/science/article/pii/S004269890...

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reactordev 2 hours ago | parent [-]

maybe in 100M years we'll get a 4th cone or rod. Probably from nuclear mutation...

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jaggederest an hour ago | parent | next [-]

We already have mutations, generally in women, for tetrachromaticism, who usually have male relatives with severe or moderate color blindness, in which the X chromosome encodes a different green cone. So they end up seeing red, strange-green, green, and blue, where strange-green is somewhere closer to red than green.

Only a few on record but they tend to have absolutely insane color matching and color perception. One of note worked in the fashion industry and could match fabrics perfectly even in varying lighting (e.g. working under fluorescent but able to match colors that would stay matched in halogen/stage lighting)

	▲	reactordev 41 minutes ago \| parent [-]
		I have that already ;) it actually looks like muddy puke green than green. However, green stop lights look more “white” than green. Some reds look like brown. I hate reds. I’m not sure about the Pantone-like color matching but I definitely see different colors than most people. To the point where my flight license is restricted. Dichromatic but not trichromatic.

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int_19h an hour ago | parent | prev [-]

There's some evidence that tetrachromacy already exists in a few humans. If so we have the gene already. But why would it spread?