Iridescence
Colour that shifts as the viewing angle changes, as on a soap bubble or a peacock feather.
Also: goniochromism, play of colour
An iridescent surface changes colour as you or it move. Soap bubbles, oil on water, the inside of shells, beetle wings and the neck of a pigeon all do it. The cause is structure, not pigment. Very thin layers or fine ridges reflect light so that some wavelengths are strengthened and others cancelled, and which ones depends on the angle. The word comes from Iris, the Greek goddess of the rainbow. Peacock feathers contain only brown pigment; their blues and greens come entirely from structure.