A horse with a solid red or brown coat is called chestnut.
Chestnut is one of the basic horse coat colors and ranges from copper-red to reddish brown, including very dark shades known as liver chestnut. The mane and tail may match the body or be lighter, but a defining feature is the absence of true black hairs in the coat. Chestnut horses are found in nearly every horse breed.
Chestnut is sometimes confused with bay. A bay horse also has a reddish or brown body, but it has black “points”—usually a black mane, tail, lower legs, and ear tips. Chestnut horses can also be mistaken for palominos when their coat is light and their mane and tail are flaxen, although palominos have a cream-dilution gene that produces a more golden appearance.
Genetically, chestnut is associated with recessive variants at the extension locus, which prevent the production of black pigment in the hair. Two chestnut horses generally produce a chestnut foal.