Dun is a coat color of horses that occurs due to the presence of a dilution gene affecting both the black and red pigments. The dun gene is responsible for lightening the body more than the primitive markings and point coloration of the ears, mane, legs, and tail. Dun horses are characterized by a dorsal stripe along the spine, horizontal stripes on the back of forelegs, a facial mask consisting of a darker patch around the forehead and nasal bone, a transverse line along the shoulders, and light hairs on either side of the mane.
The dun coat may occur in different shades, including dun (also called zebra dun, classic dun, or bay dun), red dun (also known as claybank), and grullo (also known as blue dun). Dun horses are believed to have existed as wild animals during the ancient times, as the prehistoric cave paintings in Chauvet Cave feature many equines with the dun coloration.