The iridescence of the Blue Morpho butterfly wings.

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, such as soap bubbles and butterfly wings.

Iridescence is caused by multiple reflections from multi-layered, semi-transparent surfaces where the subsequent phase shift and interference of the reflections modulates the incident light (by amplifying or attenuating different frequencies).

The word is derived in part from the Greek word ιρις (transliterated as iris, meaning stem, whose plural is ιριδες, transliterated as irides). In Greek mythology, Iris is the personification of the rainbow, who acted as a messenger of the gods.

See also thin-film optics.