The genes for skin color in mice show incomplete dominance.
Explanation:
In the field of genetics, we speak of incomplete dominance when the phenotype of heterozygous individuals is intermediate between the phenotypes of two homozygotes. This can be seen in the question where a black mouse crossed with a white mouse giving rise to a mouse with the intermediate phenotype, which is gray in color.
This is because only one copy of the active gene cannot produce the full amount of enzyme responsible for maintaining the phenotype.