Involved in the regulation of melanogenesis. The binding of ASP to MC1R precludes alpha-MSH initiated signaling and thus blocks production of cAMP, leading to a down-regulation of eumelanogenesis (brown/black pigment) and thus increasing synthesis of pheomelanin (yellow/red pigment). Causes hair follicle melanocytes to synthesize phaeomelanin instead of black or brown pigment eumelanin and produces hairs with a subapical yellow band on an otherwise black or brown background when expressed during the mid-portion of hair growth. Epithelial cells of the hair follicles and the epidermis. Widely expressed in embryonic and neonatal skin. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin.