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Friesian horses are one of the best-known breeds of black-colored horses

The Black Stallion was portrayed in film by the black Arabian stallion Cass Ole

Black is a relatively uncommon coat color in horses, though not so unusual as to be considered rare. For a horse to be considered black, it must be completely black except for white markings. A visible difference between a true black and a dark chestnut or bay is seen in the fine hairs around the eyes and muzzle; on a true black these hairs are black, even if the horse is sun-bleached, on other colors, they will be lighter.

A black horse, even with a sun-bleached hair coat (as seen with the forelock of the black horse in this image) will have solid black hairs around the eye.

A dark bay like this horse can be distinguished from a black horse by the lighter hairs around the eye.

Black is one of the two "base" color genes in horses, the other being what geneticists call the "red" gene, which creates the chestnut color. In equine coat color genetics, the black hair color is created by the extension (E) gene. This gene is dominant over red and suppresses the base red (e) gene to create an entirely black horse. Other genes may act on top of the E gene to create coat colors such as bay, buckskin, dun and gray. There is a DNA test that can detect the E gene and determine if a horse is homozygous (EE) or heterozygous (Ee) for black color.

There is a theory that there are two types of black, "fading" black and "non-fading" black. Many black horses will get sun-bleached and fade to a dark brownish color if the horse lives outside in bright sunlight on a regular basis. Non-fading black is a blue-black shade that does not fade in the sun. Genetically, the two cannot yet be differentiated, and some claim the difference occurs due to feed and management rather than genetics. The issue is hotly disputed among owners of black horses. However, it is agreed that keeping a very light horse "sheet" on a black horse in the summer will minimize fading, and feeding a well balanced diet rich in fatty acids also helps the hair coat.

Most black foals are usually born a mousy grey or dun color. As their foal coat begins to shed out, their black color will show through. While in some breeds, black foals are born jet black, in most cases, a foal born black is either actually a very dark bay or, if it has one gray parent, is apt to turn gray as it matures. A sun-bleached black horse is still black, even though it may appear to be a dark bay or brown.

Bowling, Ann T. "Coat Color Genetics: Positive Horse Identification" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed February 9, 2007