The Sky Might Not Be Blue, It Might Be a Different Color

To them, the sky might not be blue, it might be a different color. So this simplistic notion that sky is blue, ordinarily we take it as an objective fact. It's only a fact when you really qualify it in many, many ways. And i've gone, by the way, through many of these examples in my understanding relativity, part one episode. Go watch that for more examples.