It is like any other gene combination. For example in humans, blue eyes is not a dominant trait; it is a recessive trait. For a child to have blue eyes, both the mom and the dad must contribute the gene for blue eyes. If the mom and the dad are both blue eyed themseves, then the ONLY genes they have are blue. If the mom is brown eyed, she may have 2 brown eye genes, OR she may have one brown eye gene and one blue eye gene; and as brown is the dominant trait, the brown is the color of HER eyes. The blue eye gene is recessive and does not show. But she could pass a blue eye gene to a child of hers. If the dad also has brown eyes, but carries one of each gene, they the 2 brown eyed parents could have a blue eyed child. So yes, a pair of black labs could have a yellow lab pup.