What happens if a dark-colored dog carries the mask gene?

If a dark-colored Great Dane—such as a solid black, blue, harlequin, or merle—carries the mask gene, the mask will be completely hidden and not visually noticeable.

The masking trait (the E 

M

  allele on the E-locus) is dominant and produces dark pigment on the dog’s face. Because the mask itself is dark, it simply blends in with the dog’s existing dark base color or heavy spotting pattern.

Even though the mask cannot be seen on a dark-colored dog, the dog can still carry the dominant gene and pass it on to its puppies. The mask will only become visually apparent if the offspring inherit the gene alongside a lighter base coat, such as fawn or brindle. Because the trait can be completely camouflaged by a dark coat, breeders must rely on DNA testing to reveal if a dark-colored dog secretly carries the mask gene.