Colors of the Sunset-What Determines Sky's Color?

The colors of the sunset & sunrise result from a phenomenon called scattering. Molecules and small particles in the atmosphere change the direction of light rays, causing them to scatter and resulting in colorful sunsets/sunrise. But the details are determined by the wavelength of the light and size of the particle.
The short-wavelength blue and violet are scattered by molecules in the air much more than other colors of the spectrum. This is why blue and violet light reaches our eyes from all directions on a clear day. But because we can't see violet very well, the sky appears blue.

If the path is long enough, all of the blue and violet light scatters out of your line of sight. The other colors continue on their way to your eyes. This is why sunsets are often yellow, orange, and red." Red has the longest wavelength of any visible light. The sun is red when it's on the horizon, where its extremely long path through the atmosphere blocks all other colors.

According to StevenAckerman, Professor of Meterology at UW-Madison.