Polychroism

Part of speech: noun

Definitions

1. The occurrence where certain materials reflect or transmit varying colors as a result of changes in viewing angle or light conditions
2. A characteristic of specific substances that leads to the perception of different colors depending on the angle of illumination or observation
3. The property of some materials to present multiple colors when seen from various angles or under different lighting

Etymology: The word is built from Greek "polys," meaning "many," and "chroma," meaning "color," with the suffix "-ism" marking a condition or phenomenon. Its closest relative is the mineralogists' "pleochroism," which uses the Greek "pleion," meaning "more," for the same idea: a crystal that shows different colors when viewed from different directions. That shared idea of color that depends on the viewer's angle is what makes gems such as tourmaline and iolite seem to change hue as they are turned. Polychroism is the broader label, applied to any material whose color shifts with angle or lighting, while the mineralogists' term is restricted to crystals.