Unique colorant compositions, well suited for the pigmentation of a wide variety of coatings and substrates, e.g., cosmetics, plastics, paints and rubbers, comprise (1) at least one crystalline rare earth metal sulfide or sesquisulfide, for example cubic cerium sesquisulfide Ce.sub.2 S.sub.3, and (2) a dopant amount of at least one alkali metal, and wherein the at least one rare earth metal sulfide or sesquisulfide comprises whole (unground) monocrystalline grains thereof having a mean particle size of at most 1.5 .mu.m.