Calico cats (also known as tortoiseshell-and-white) are special, not only for their distinctive tri-colour fur, but for the fact that they are almost always female. When a rare male is born with calico markings, he will generally be sterile.
Here are two lovely examples of calico cats. The first belongs to a good friend of mine. The other I spotted while out walking and felt I needed to take a photo, as the markings were really unusual.