Dun is a particular color pattern found in horses characterized by less intense coat color and a dark stripe down the spine. Dun was originally defined as being a neutral gray-brown, but horses of that exact color may or may not possess the dun gene responsible for the pattern.
Dun horses under the modern definition can be of any coat color, including red and black. Many but not all dun horses also have dark markings on their legs and faces that are the same shade as the stripe on their backs. Sometimes the legs display horizontal stripes, similar to the markings on a zebra but with much lower contrast. Black dun is also called grullo.