Two alleles at the black locus in the red flour beetle Tribolium castaneum (Herbst) have been resolved. Dusky (bd), the lighter-colored of the two, is dominant to tawny (bt), the darker. Both are recessive to wild-type and codominant with black (b). A revision of the multiple allelic series at the black locus is proposed, encompassing five phenotypically distinct alleles described by a five-hue color series. The hues represent the practical limit of resolution of alleles by visible phenotype.