Iridescence

Iridescence, as defined by Wikipedia:

Iridescence is an optical phenomenon characterized as the property of surfaces in which hue changes according to the angle from which the surface is viewed (as may be seen of soap bubbles and butterfly wings).

Iridescence is caused by multiple reflections from multilayered, semitransparent surfaces in which phase shift and interference of the reflections modulates the incident light (by amplifying or attenuating some frequencies more than others). This process is the functional analogue of selective wavelength attenuation as seen with the Fabry-Pérot interferometer.

The word is derived in part from the Greek word iris (pl. irides), meaning "rainbow," which in turn derives from the goddess Iris of Greek mythology, who personifies the rainbow and acts as a messenger of the gods.

Because the apparent image changes with the angle of observation, iridescence is not reproduced by conventional still image photography. It can be reproduced, however, by holography (which includes phase information).

Or, perhaps even more succinctly:

Iridescence: a lustrous rainbowlike play of color caused by differential refraction of light waves (as from an oil slick, soap bubble, or fish scales) that tends to change as the angle of view changes.