You guys are excellent help, so I have come to consult with you again.
My ancient peoples used to live during the day, but became nocturnal due to a variety of reasons. Iâm at loss on how a loss of nuanced, three colour based colour vision in favour of better night vision would be reflected in the language of those people.
Say that they become red-green blind, over generations, and we return to them a long time in the future. Would they still use the word âredâ to refer to e.g. blood, and âgreenâ for plants and the like, or would they call both of those brown if dark and yellow if bright? Would they use the terms because the language has assigned those terms to things, such as grass or blood, even though they are no longer distinguishable? And how can I reflect that in writing? I could say âher blood was the same colour as the grass as it flowed out from her bodyâ, but wouldnât that just be really confusing?
Feral:Â Â You have accidentally stumbled into a major, controversial debate, my friend. One that I happen to live for.
There are two general theories on how names for colors develop and how those words interact with culture.
Universalism describes a general trend in the development of color words across all cultures. First there are words for white and black or dark and light, then red, then green and yellow, then blue, then grey, brown, purple, pink, orange, teal, etc and then finally super specific things like Sherwin-Williams paint colors. This is despite any environmental reasons one might develop color words out of order.
Relativism (youâll also see Whorfianism) describes the effect on the development of color words based on environmental factors and the effect the existence of those color words has on individualsâ abilities to differentiate between colors. For example, a community that has two colors of flowers growing wild near them, one of which is pink and is good to eat and one of which is orange and is deadly if ingested, would logically figure out an efficient way to describe them, in this case with color words, and would logically also become better at differentiating between the colors, especially if they are on a spectrum that can get very close to one another.
Homerâs reference to the âwine-dark seaâ in The Odyssey gets pointed to a lot in this debate. Universalists will tell you that when Homer, or whoever, composed The Odyssey, Greek had not yet developed beyond the dark/light or dark/light and red stage; thus, Homer was describing it based on terms of light/dark and the wine reference is more about its viscosity. Relativists have been known to argue that Ancient Greeks were blue color blind.Â
As with most binaries, the answer falls somewhere in the middle of whatâs actually a spectrum. But as a world-building tool, it can be really helpful to take a stance somewhat close to one of the extremes.Â
Iâve done a lot of research on this particular topic, but unfortunately, due to its academic nature, a lot of that is behind paywalls. Here are some free resources to get you started: Â Â
Wikipedia: Lignuistic Relativity and the Color Naming Debate Â
Sapiens: Do You See What I See by Nicola Jones Â
APA: Hues and Views by Rachel AdelsonÂ
Berkeley.Edu: Language, Thought, and Color by Terry Regier and Paul Kay  side note: Paul Kay is one of the go-to researchers on this topic if you can find more by himÂ
Color Blind Awareness  will probably also be helpful for you to reference.Â
As for your specific query, I strongly caution against saying that her blood is the same color as grass. Iâve worked with a number of color-blind clients and I am fully aware of that 1 in 12 men and 1 in 200 women are color-blind, Iâm still gonna assume if Iâm reading a fantasy novel that the blood is just green. And if youâre saying itâs both red and green, Iâm just going to be confused. It would be much clearer immediately if they simply didnât have color words for red and green, or share a color word for them, and someone from the outside introduces the concept that they are two different colors, preferably before anyone is bleeding out. Â Â
Another thing that might be helpful for you to research is the etymology of modern color words in as many languages as you can to realistically project how your new language has evolved from the ancient language. âGreen,â for example, traces back to exactly what you assumed it does, the PIE root *ghre- meaning âgrowâ or âthe color of growing plants.â (and don't get me started on the etymology and history of "blue"; it is legit wild),
Back on topic, your people might refer to red as âbloodâ and also the color of grass as âbloodâ (or vice versa depending on the culture, but based on Universalism, as environmental factors should not be an issue, it would be âbloodâ) which a Relativist would love because it gives a really fascinating look into the psychology of culture and its relationship to the earth and vegetation. Or, as you posited, especially if thereâs no plot or character related reason for the names of colors to be a thing, just dark vs light works totally fine, Universalist or Relativist.