Color is one of the intrinsic properties of something material. We perceive its color because some light reflected from it reaches our eyes. The smallest unit of matter with specific properties is a molecule. All matter in the universe represents conglomeration of different types of molecules in diverse configurations. How light gets affected by material in its path depends on the size of the material. There are four basic processes that light goes through when it falls on an object. These are reflection, refraction, diffraction, and scattering. Of these only scattering is of any consequence when tiny particles like molecules are involved.

On a bright clear day the sky appears blue. This happens because the earth has a gaseous atmosphere in which oxygen and nitrogen are the dominant components. When the light from the sun hits the nitrogen and oxygen molecules it is scattered in all directions. By light we normally mean the visible part of electromagnetic radiation. The light from the sun contains the seven primary colors from violet to red. The color depends on the frequency or the wavelength of the radiation. The wavelength increases from violet to red, while the frequency decreases. For particles comparable to the wavelength of light the scattering depends on the wavelength. The shorter the wavelength, the larger is the amount of scattering.

The human eye senses color mainly through three primary colors