What Is Iridescence?
Iridescence is an angle-dependent visual effect: the apparent color or brightness of a surface changes as the light, surface, or viewer moves. A soap bubble, an oil film, a compact disc, and some insect wings are familiar examples.
Color made by structure
Pigments absorb some wavelengths and reflect others. Structural color instead comes from microscopic features that interfere with, scatter, or diffract light. The observed result depends on feature spacing, orientation, and the geometry between the light source, surface, and viewer.
Why the color moves
Think of the surface as a field of extremely fine optical traffic directors. Changing the viewing angle changes which wavelengths are directed toward the eye, so a mark may shift hue, become brighter, or disappear even though the material itself has not changed.
Iridescent is not a fixed color
A camera RGB value records one observation under one optical arrangement. It is useful as a calibrated lookup for that arrangement, but it is not a universal paint-chip specification. Always evaluate the result under the lighting and viewing conditions relevant to the finished work.