"Why is the sky blue?"
Well, I was always told that the sky wasn't blue, and that it was just the sun reflecting off of the ocean, making the sky seem blue, but others have told me that it is not the ocean that is reflecting off of the sky, but something called blue light. Basically, blue light is strewn in all directions by the extremely small molecules of air in the Earth's atmosphere, making the sky seem blue. When the sky is not blue, like, if its violet or something, it is because of the violet lights that reflect from the sun.
~Hope I helped!~