Highland Ponies are seen in a range of dun shades. The Highland Pony Society recognizes shade variations referred to as "mouse" (known in other breeds as grullo), "yellow" (bay dun), "grey" (dun with gray gene that lightens with age), and "cream" (a dun apparently also possessing a dilution factor). Other, nonstandard terms, such as "fox dun", (describing a red dun) "oatmeal dun", and "biscuit dun" (describing a cream dun) are sometimes also used. They also may be grey, seal brown, black, and occasionally bay or a shade of liver chestnut with a flaxen mane and tail.