More specifically, it is believed by historians/biologists that humans didn't evolve the ability to distinguish between shades of blue until relatively recently. The ocean and the sky are 2 of the only examples, and humans didn't spend much time in either place. A few fruits are blue, a few poisonous animals might have some blue, but the vast majority of natural things aren't blue. We have examples of ancient writings comparing the color of the ocean to the color of wine. Even now, our eyes have the fewest cones for detecting blue wavelengths, and the most for distinguishing greens. Graphical artists have to account for this literally all the time. Every digital color space we've made saves some bits by shifting more color resolution to greens and reds because no one will notice the extra blues.
It's not biological evolution, but linguistic evolution at play. There's a specific evolutionary pattern for color words in language found for the most part (albeit like everything in language and evolution, there's always exceptions to the pattern):
All language known have terms for black and white.
If a language has three color terms, the third is 'red'.
If a language has four color terms, the fourth is either 'green' or 'yellow'.
If a language has five color terms, the fifth is the other of 'green' or 'yellow'.
If a language has six terms, the sixth is 'blue'.
If a language has seven terms, the seventh is 'brown'.
And from there it starts to heavily diverge with purple, pink, orange, grey.
Not sure what you mean by, "It's not biological evolution". The linguistic phenomenon you're referencing doesn't make any sense outside the context of the specific evolutionary history of the human eye. It would be like saying the shape of something has nothing to do with the shadow it casts.
Sure it does, because there's languages in use today that don't separate blue from green, and those native speakers absolutely have blue cones in addition to green and red ones. Language development is fairly universally thought to have happened after we evolved our blue sensing cones, so that doesn't explain the difference. Specifically we evolved blue cones about 30 million years ago, before we were any semblance of human.
The thought is that it's a phenomenon that by giving a name to the concept and training your young, our brains become better at differentiating it at a conscious level. The progression in language is thought to be an artifact of how strongly the differences between naturally occut colors appear to our brains, and an innate way to separate the state space of natural color rather than a purely mirroring of biological evolution of color sensing hardware in the eye.
What do you mean humans did not spend time in that place? Every human being sees the blue sky as at least 30% of what they saw everyday starting at birth.
Water is "actually" blue, as in due to the chemistry of its electronic configuration. A deep column of water has a blue color in a way that other liquids, such as benzene, do not. There was a cool picture of this demonstration in one of my old chemistry books.
Reflection of the sky accounts for much of the color of natural bodies of water, but it's cool to know that it's blue even in the absence of blue reflection.
I think the explanation is that it didn't occur very often, until recently, as a dye or pigment. Color terms are more useful to describe things, like shirts, that don't have an inherent color. In a society where everything just has its inherent color, you don't need many color terms. In a society where people can change things' colors, these terms are more useful.
