Three coat colors are recognized for Rough Collies: sable and white, where the "sable" ranges from pale tan to a mahogany; tricolour, which is primarily black edged in tan; blue merle, which is mottled gray. All have white coat areas, in the collar, parts of the leg, and usually the tail tip. Some may have white blazes on their faces. In addition, the American Kennel Club accepts white, where the dog is predominantly white with colored markings of sable, tricolor, or blue merle on the head and sometimes body patches. Rough Collies have a blunter face than the smaller, but otherwise very similar Shetland Sheepdog, which is partly descended from the Rough Collie. The planes of the muzzle and the top of the skull should be parallel in collies, with a slight but distinct stop. (In shelties, the planes are not parallel.) The downy undercoat is covered by a long, dense, coarse outer coat with a notable ruff around the neck, feathers about the legs, a petticoat on the abdomen, and a frill on the hindquarters.