Luster describes the way pearls seem to glow from within. It's based on the depth of reflection due to the layering of the aragonite crystal.

Overtone describes the translucent "coating" of color that some pearls have. A silver pearl may have a blue overtone or a green overtone, for example. Orient, sometimes called iridescent orient, describes the variable play of colors across the surface of the pearl like a rainbow. While not all pearls have iridescent orient, freshwater pearls are known for their dramatic orient.