The term 'shimmer colorfully' can be summarized by the word 'opalesce, ' which is an 8-letter word. Opalescence is a phenomenon in which an object appears to have a milky, iridescent sheen or glow. This effect is often seen in precious stones such as opals, moonstones, and pearls, as well as certain minerals and metals. It is caused by the diffraction of light off of tiny particles within the material.