On a clear day the sky is blue to deep blue. At dawn and dusk the stretch of sky nearest the sun changes to shades of red, orange and yellow. The color of the sky is primarily determined by the way air molecules scatter light relative to the sun's angle.
Visible light arrives at Earth as full-spectrum, white light, composed of all colors. The Rayleigh scattering phenomenon explains the tendency of Earth's atmosphere to scatter and spread blue light more than green or red light. Nitrogen and oxygen molecules make up most of the atmosphere, which absorbs and reflects the majority of these other colors before they reach the surface. Other factors affecting the sky's color include materials and pollutants in the air and the anatomy of the human eye.