A tortoiseshell cat is a cat with a coat coloring named for its similarity to tortoiseshell pattern. The coat pattern is made up of mottled patches of black, chocolate or grey along with red or cream. Tortoiseshell cats are almost exclusively female, and male tortoiseshells are rare and are usually sterile. The term “tortoiseshell” is usually reserved for multicolored cats that have rather small or no white markings.