Transporter that mediates the import of cysteine into melanosomes, thereby regulating skin/hair pigmentation. In melanosomes, cysteine import is required both for normal levels of cystine, the oxidized dimer of cysteine, and provide cysteine for the production of the cysteinyldopas used in pheomelanin synthesis, thereby regulating skin/hair pigmentation. Also catalyzes import of cysteine into lysosomes in non-pigmented cells. L-cysteine(in) = L-cysteine(out) Genetic variants in MFSD12 cause skin/hair pigmentation variations and are the cause of mushroom coat color in shetland ponies. Belongs to the major facilitator superfamily.