What Causes a Sunset to Appear in Different Colors?

Imagine you're looking at a big, bright ball (the Sun) that is slowly going down behind the Earth. When it's high up in the sky, it looks white or blue because its light travels through less air. But as it goes lower, the light has to travel through more air, and different colors of light get scattered in different ways, reds and oranges come out on top, making the sky look like a painting.