a loss or inactivation of the gray allele in some of the somatic cells as that would explain why the speckles are more common on heterozygous grays than homozygotes. Melanoma in gray horses The identification of the gray mutation is of great interest in of medical research since this mutation also enhances the risk for melanoma in horses: some studies have suggested as many as 80% of grays over 15 years of age have some form of melanoma. Growth rate depends on the type, and many are slow-growing, but over time, many develop into a malignant melanoma. The study of gray genetics has pointed to a molecular pathway that may lead to tumour development. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from gray horses, and those carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses. Some studies indicate as many as 66% of melanomas become malignant, though other studies have found much lower rates, and in one case, zero. Horse coat colors sometimes confused with gray White horses Many people who are unfamiliar with horses refer to a gray horse as "white". However, most white horses have pink skin and some have blue eyes. A horse with dark skin and dark eyes under a white hair coat is gray. However, a gray horse with an underlying homozygous cream base coat color may be born with rosy-pink skin, blue eyes and near-white hair. In such cases, DNA testing may clarify the genetics of the horse. Roan Some grays in intermediate stages of graying may be confused with a roan or a rabicano. Some heavily fleabitten grays may also be confused with roans. However, roans are easily distinguishable from grays: roan consists of individual white hairs on a dark base coat, usually with the head and legs of the horse darker than the rest of the body. Rabicanos also have intermixed white hairs primarily on the body with a dark head. With gray horses, the head is often the first area to lighten, especially around the eyes and muzzle. Also, roans do not lighten with age, while grays always do. The varnish roan is another unusual coloration, sometimes seen in Appaloosa horses, that, like gray, can change with age, but unlike gray, the horse does not become progressively lighter until