You know, I asked this once in some environmental science course and got the answer that it has something to do with how light refracts off of water particles in the atmosphere or something like that, but really it’s because the sky would look weird any other color.
Just think: purple would make people sad.
Green seems ominous in a Wizard of Oz, impending tornado kind of way.
Red is damn near apocalyptic–and orange isn’t much better if we’re being serious.
The sky’s already black at night, and white would probably burn out our corneas.
Yellow means that we couldn’t see the sun…so really, that just leaves blue.
It just makes sense.