Why is the sky blue ?

I don't suppose you happen to know
Why the sky is blue ? It's because the snow
Takes out the white. That leaves it clean
For the trees and grass to take out the green.
Then pears and bananas start to mellow
And bit by bit they take out the yellow.
The sunsets, of course, take out the red
And pour it into the ocean bed
Or behind the mountains in the west.
You take all that out and the rest
Couldn't be anything else but blue.
--Look for yourself. You can see it's true.

WHY THE SKY IS BLUE
John Ciardi

This is a fun way to explain why the sky is blue, but it isn't true, of course. The sky really gets its color from the sunlight passing through the air.

Sunlight contains all the colors of the rainbow. These colors are scattered as they pass through the air. The color blue is scattered most of all. On a clear day, the molecules of gas in the air make the blue scatter. It is reflected into our eyes from all parts of the sky. So the sky looks bright blue.

But at sunrise or sunset, the sun's light comes to us through all the hot, dusty, smoky air close to the ground. The smoke and dust make other colors, such as yellow and red, scatter. Then, the sky seems pink or red, and the sun is a big orange ball.