In the atmosphere, it isn't chalk dust or flour that scatters, but the different kinds of molecules that make up the air. Light is made up of all the colors of the rainbow, each with its own wavelength. This is called the electromagnetic spectrum. When the path length of sunlight is the shortest, the middle of the day, the sky is blue, because of shorter wavelengths being scattered. At sunrise and sunset, when the sun has more distance to travel through the atmosphere, the shorter wavelengths are scattered out, leaving the longer oranges and reds.
Refraction is the bending of light as it passes through two materials of different density.
As the light passes from the less dense air to the more dense water, it slows down. This is why it is hard to spear a fish or pick up an object in the bottom of an aquarium. The refraction also causes the light to separate into colors. White light is composed of all of the colors. Students can study the Law of Reflection and Law of Refraction to better understand the optics involved in atmospheric phenomenon.