Neutral (white) light is composed of radiation of all the wavelengths between 380 nm. and 760 nm. If a white ray of light passes through a prism, its components will be deflected to varying degrees by the process of diffraction. A band of light will become visible, possessing the colors of the rainbow and known as the spectrum. The spectrum begins with red and the long-wave end, changes through yellow and green at its medium-wave center, ending with violet at the short-wave end. This physical spectrum continues at its infrared and ultraviolet ends, although the radiation there is invisible to us.

—Color Systems in Art and Science, edited by Klaus Stromer, translated from the German by Randy Cassada, 1999.