The Sun produces white light which can be separated by a prism into the colors of the spectrum each with a different wavelength. During the day air molecules act as a prism separating the colors of white light so that we only see the shorter wavelength blue colors and the sky appears blue. In the morning and evening the Sun is at a different angle to the Earth. This lower angle of the Sun along with dust and debris in the atmosphere scatter white light so that we see the longer wavelengths of yellow, orange, and red. Therefore, we see the beautiful colors at sunrise and sunset. Sadly the more air pollution the greater the intensity of color at sunset.