According to VetGen, a black lab and a chocolate Labrador Retriever crossed together can potentially produce all three colors of the breed: black, chocolate and yellow. The results of the cross ultimately depend on the genes carried by each lab.
Two pairs of dominant and recessive alleles, or alternate forms of a gene, work together to produce coat color in Labrador Retrievers. The dominant allele of one pair, conventionally represented as an uppercase "B," yields a black coat color, and the recessive allele, conventionally represented with a lowercase "b," yields a chocolate coat color. Every lab has two alleles for this gene, one from each of its parents.
A dog with the "B" allele always expresses a black coat color, but it can potentially pass a "b" gene to its progeny if it receives one from its parents. The second gene is typically represented with uppercase "E" and lowercase "e" for the dominant and recessive gene respectively. This gene determines whether the lab's pigment extends to the coat. A lab that receives two recessive "e" alleles is always yellow, regardless of its genotype with respect to the "B" set of alleles, whereas a lab with at least one "E" allele always expresses a black or chocolate coat color.