Tortoiseshell is a cat coat coloring named for its similarity to
tortoiseshell pattern. Like tortoiseshell-and-white or calico cats,
tortoiseshell cats are almost exclusively female. Male tortoiseshells
are rare and are usually sterile.
Tortoiseshell cats, or torties, combine two colors other than white,
either closely mixed or in larger patches. The colors are often
described as red and black, but the "red" patches can instead be orange,
yellow, or cream, and the "black" can instead be chocolate, gray, tabby,
or blue. Tortoiseshell cats with the tabby pattern as one of their
colors are sometimes referred to as torbies or torbie cats.
"Tortoiseshell" is typically reserved for multicolored cats with
relatively small or no white markings. Those that are predominantly
white with tortoiseshell patches are described as tricolor,
tortoiseshell-and-white, or calico (in Canada and the United States).
Tortoiseshell markings appear in many different breeds, as well as in
non-purebred domestic cats. This pattern is especially preferred in the
Japanese Bobtail breed, and exists in the Cornish Rex group.