"Why is the sky blue and not purple?"
How AskOwlo explains it:
"Imagine sunlight is like a box of crayons with ALL the colors mixed together. When sunlight hits the air, the tiny bits of air play with the colors like a game. Blue is their favorite color to bounce around! That's why we see blue everywhere when we look up. Purple is in there too, but our eyes are better at seeing blue—so blue wins!"