 Puppies of all colours can potentially occur in the same litter . Colour is determined primarily by three genes . The first gene ( the B locus ) determines the density of the coat 's eumelanin pigment granules , if that pigment is allowed : dense granules result in a black coat , sparse ones give a chocolate coat . The second ( E ) locus determines whether the eumelanin is produced at all . A dog with the recessive e allele will produce only <unk> pigment and will be yellow regardless of its genotype at the B locus . The genes known about previously have had their number increased by the introduction of the K locus , where the dominant " black " allele KB is now known to reside . Black or chocolate Labradors therefore must have the KB allele . Yellow Labradors are determined at the E locus , so the K locus is irrelevant in determining their colour . Variations in numerous other genes control the subtler details of the coat 's colouration , which in yellow Labradors varies from white to light gold to a fox red . Chocolate and black Labradors ' noses will match the coat colour . 
