Blue is the last color that cultures name, because it’s difficult to create blue dyes or paints. Until we name a color, we cannot perceive it. What color is the sky to cultures that have not yet named blue? Generally, they see it as white or black, sometimes without any color at all. Not blue. I don’t mean that they don’t call it “blue,” I mean that they *actually* see it as white or black.
We westerners saw the sky as colorless until a couple of thousand years ago, when we learned to create blue paint and dye from lapis lazuli, which remained rare and enormously expensive until a cheaper blue dye was discovered in the Americas. The ancient Greeks, in all of their writings, not once declared the color of the sky to be “blue,” because they simply didn’t have that color.