Opalescent

Etymology

Built from "opal" plus the Latin-derived suffix -escent (from -escentem, "becoming" or "beginning to be"). "Opal" itself comes through Latin "opalus" from Greek "opallios," and is often traced further to Sanskrit "upala" (stone, gem). The whole word thus means "becoming opal-like," coined in the nineteenth century as the science of light and color matured.

adjective · /oh-puh-LESS-uhnt/
Showing a soft, milky play of shifting colors, like an opal.
What it names
A precise word for the inner, cloudy shimmer of moonstone, opal, or certain skies and seas — not flashy iridescence but a gentler glow.
Example
At dawn the mist over the lake turned opalescent, pink and silver bleeding into one another.
Related idea
Iridescent colors shift sharply with the angle, like a soap bubble or beetle shell; opalescent light is the softer, milkier inner glow of an opal or moonstone.