Abstract: Novel colorant/pigment compositions, prepared via precipitation technique and well suited for the coloration of a wide variety of materials and substrates, e.g., plastics, paints and inks, ceramics, cosmetics, etc., comprise composite core/sheath particulates, the cores of which comprising particles of at least one crystalline rare earth metal sesquisulfide having the formula M.sub.2 S.sub.3 in which M is at least one lanthanide element having an atomic number of from 57 to 71, or yttrium, and such core particles having at least one alkali and/or alkaline earth metal dopant at least in part incorporated within the crystal lattice of the at least one crystalline rare earth metal sesquisulfide, and each sheath comprising a coating layer of at least one transparent oxide deposited onto the external face surfaces of the doped core particles.