Raven, how do you like me now?
Showing your ignorance yet again. Nothing there says we saw it as clear or that blue was 'invented'. If the sky had been clear, we'd just see the sky as . . . black, which we'd never have identified with a hypothetical clear glaze that somehow later became called blue. Plus, you said 400 years, and even the article says the first mention of blue in a language was from 4,500 years.