“The possibility of producing light of a single wavelength (coherent light) by means of the laser, developed in the 1960s, made it possible for the first time to produce on a flat surface images of considerable depth. Coherent light is, of course, monochromatic, and all early holograms were likewise monochromatic, usually recorded and replayed with light of the longer wavelengths, red or yellow. But in 1969 the American holographer Stephen Benton devised a method for recording all the spectral colours in a single hologram, which he called the ‘Rainbow Hologram’, and it is this type, which can only represent a relatively shallow space, that is familiar to us from banknotes or credit cards.”

—John Gage, from Color in Art, 2006.