Because the perception of color is mostly a neurophysiological function between the eyes and the brain, it can vary slightly from person to person. Further, the subtractive color seen depends on the light source. If you plan to paint a room you should examine the color when illuminated by several different lights sources: sunlight, light from incandescent lamps, and light from fluorescent lamps. The colors may look very different. They will even look different in the sunlight at noon versus that near sunset. Scientists, artists, advertisers, and printers need an objective method of specifying color as it relates to the frequency of light. This technique for measuring the intensity of particular wavelengths of light is known as colorimetry.

Hue is related to the wavelength of a color. Saturation is the extent to which other wavelengths of light are present in a particular color. For example for the hue red, deep red is saturated, but pink is a mixture of red and white.