"Cerulean" comes from the Latin word "caeruleus," which means "dark blue" and is most likely from "caelum," the Latin word for "sky." An artist rendering a sky of blue in oils or watercolors might choose a tube of cerulean blue pigment. Birdwatchers in the eastern U.S. might look skyward and see a cerulean warbler (Dendroica cerulea). "Cerulean" is not the only color name that’s closely associated with the sky. "Azure" (which ultimately comes from a Persian word for lapis lazuli, a rich blue stone) describes the color of a cloudless sky and can even be a noun meaning "the unclouded sky."