The Rat Terrier comes in a variety of coat colors. The classic coloring is black tan point with piebald spotting (known as black tricolor), but chocolate, tan (varying in shade from pale gold to dark mahogany), blue, isabella (pearl), lemon and apricot are all fairly common. They may be tricolor or bicolor, always with some amount of white present. Sable may overlay any of these colors. Creeping tan (often 'Calico'), is also acceptable. Ticking is usually visible in the white parts of the coat, or in the underlying skin. Brindle, currently disallowed by the main breed standards, is considered by some to be a traditional Rat Terrier pattern, and there is a growing movement to have this pattern accepted into the breed. However, merle is widely considered to be the result of recent outcrosses and, because of associated health problems, is rejected by most Rat Terrier breeders.