Dilution gene in the context of "Gray (horse)"

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. 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."