A detailed comparative study of the optical properties of two rare‐earth (RE) sesquisulfide compounds &ggr;−Ce2S3and &ggr;−Gd2S3, shows that if the two compounds have about the same main absorption edge corresponding to band‐to‐band S 3p‐RE 5dtransitions, Ce2S3exhibits an additional absorption band at lower energies. This band, which is ascribed to the presence of Ce 4fstates at the top of the valence band, explains the difference in color between the two compounds. ©1996 American Institute of Physics.