Grey as a metal; yellow, beige or pink as cerium oxide.
As a metal it’s highly reactive; oxidizes quickly when exposed to air. Cerium oxide is seen as very stable; it produces a powerful light when heated.
Cerium is used for coating exhaust gas catalysts, as a polish for optical glasses, as a UV absorber, e.g. in windscreens, or for staining and decolouring glass.