The calico cat is neither a breed nor a mutation in the cat world it is a color pattern. A cat whose coat color contains white, black and orange is designated a calico.
For a simple explanation, this is a genetic trait usually passed on to the female but occasionally found in males cats. When a male is calico it has XXY chromosomes it renders him sterile.
There are two main color variations, calico and tortoiseshell. The tortoiseshell can be diluted or muted. The calico can be white with patches of black and orange. The tortoiseshell is a brindled color with blue, black and orange. The diluted or muted tortoiseshell fur is lilac, grey, and cream.
This coloration is found in many breeds including the American Shorthaired Cat. Several other breeds have accepted this pattern as part of the standard like the Japanese Bobtail.
The origin of the coloration is not clear. Many countries consider male calico cats a good luck charm. Japanese fishermen kept them on board to frighten ghosts. For the Milwaukee cat owner, they are just part of the family.