How the Sky and Clouds Choose Their Colors.
There are no colors being sent to the earth through or from the atmosphere. Surprised? It's true. The atmosphere itself has no color at all. What we see when we look into a clear blue sky, or when we're awed by gorgeous sunrises and sunsets are light waves reflected off dust particles and air molecules. Not terribly romantic, but it doesn't prevent us from enjoying a spectacular sight.
Got the Blues? That's Good!
The size of the wavelengths determine the colors we see. A blue sky comes from the shorter wavelength of violet and blue waves. These shorter waves are scattered more efficiently than the less visible reds and oranges. The amount of water vapor in the atmosphere determines the depth of the color. Water vapor creates a veil overhead. The thinner the veil, the brighter the blue.
White or Gray?
Clouds are white because the water that creates them scatters color away from the cloud area. The sun's light is reflected off the clouds in degrees based on the density of the water vapor in the clouds. The darkest gray or black clouds are the ones having the highest concentration of water vapor and are naturally less reflective.
Nothing but Blue Skies? The sun is close to the horizon when rising and setting. The low angle allows the orange and red light waves their opportunity to be seen. Floating particles from pollution, dust, or ash can enhance and deepen the colors reflected in the low sun. Although dirty air is undesirable, for right or wrong, sunsets and bright blue skies wouldn't be nearly as intense without at least a little airborne debris.