| Gray horse | |
|---|---|
 A young gray Lipizzan horse. Grays are typically born a darker color, and their hair coat will be pure white before they are 10 years old as they age | |
| Other names | Grey |
| Variants |
|
| Genotype | |
| Base color | Any |
| Modifying genes | Graying gene (G) dominant when single allele present |
| Phenotype | |
| Body | Born any color, lightens with age until fully white, may develop pigmented speckles |
| Head and Legs | Head may be first part of body to lighten, legs may be among last parts of body to lighten |
| Mane and tail | May not gray at same rate as body, can be lighter or darker |
| Skin | Usually black, except under white markings present at birth. |
| Eyes | Usually dark brown, unless affected by other genes which lighten eye color |
| Other notes | When gray gene is present, horse will always become gray, may be masked by white genetics |
A gray horse (or grey horse) has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color.[1] Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.
The stages of graying vary widely. Some horses develop a dappled pattern for a period of time, others resemble a roan with more uniform intermixing of light and dark hairs. As they age, some gray horses, particularly those heterozygous for the gray gene, may develop pigmented speckles in addition to a white coat, a pattern colloquially called a "fleabitten gray."
Gray horses appear in many breeds, though the color is most commonly seen in breeds descended from Arabian ancestors. Some breeds that have large numbers of gray-colored horses include the Thoroughbred, the Arabian, the American Quarter Horse and the Welsh pony. Breeds with a very high prevalence of gray include the Percheron, the Andalusian, and the Lipizzaner.
People who are unfamiliar with horses may refer to gray horses as "white". However, a gray horse whose hair coat is completely "white" will still have black skin (except under markings that were white at birth) and dark eyes. This is how to discern a gray horse from a white horse. White horses usually have pink skin and sometimes even have blue eyes. Young horses with hair coats consisting of a mixture of colored and gray or white hairs are sometimes confused with roan. Some horses that carry dilution genes may also be confused with white or gray.
While gray is classified as a coat color by breed registries, genetically it may be more correct to call it a depigmentation pattern. It is a dominant allele,[1] and thus a horse needs only one copy of the gray allele, that is, heterozygous, to be gray in color. A homozygous gray horse, one carrying two gray alleles, will always produce gray foals.