Little is known about the specific genes that contribute to the variations in human skin color. An exciting clue has now emerged from an unlikely source, a tiny aquarium fish. Working with a mutant line of zebrafish called golden, whose stripes are paler than those in wild-type fish, Lamason et al. found that the altered pigmentation was caused by a mutation in the slc24A5 gene, which encodes a protein potentially involved in cation exchange. The gene is highly conserved in vertebrates, and expression of the human gene in the golden zebrafish restored wild-type pigmentation. European populations carry a slightly different version of the slc24A5 gene than do African and East Asian populations. A genetic polymorphism that changes one amino acid in the coding region of the gene correlates with skin pigmentation levels, which suggests that slc24A5 may contribute to skin color in humans.