dogs have a nerve in there body that gives them the color of there coat and there coat.

Chestnut

(copied from wikipedia) Grulla is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. In this coloration each individual hair is mouse-colored, unlike a roan which is composed of a mixture of dark and light hairs.

Probably the only truly rare coat "color" is brindle. The occurance of this coat color pattern is so rare that there is still debate on how it is inherited.

Calico is a coat color, not a breed. Tabby is also a coat color, not a breed.

Red and white alleles for coat color are alternative forms of a gene that determine the color of an organism's coat. The red allele typically produces a red or orange coat color, while the white allele produces a coat color that is primarily white. The presence of these alleles, and the dominance or recessiveness of each, will determine the coat color of an individual organism.