Grullo

Grullo[1] (pronounced GREW-yo)[2][a] or grulla is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs.

If a grulla also carries the gray gene, it will be born a mouse tan-gray shade, usually with bold primitive markings, but then lighten and eventually develop a white hair coat with age.

[2] In the Norwegian Fjord horse, the coat is called grå (meaning "gray").

However, some authorities in the early twentieth century held the opinion that most equines called tarpans were actually domestic or feral horses, not a separate species.

One of the first experiments in this regard was published in 1906 by James Cossar Ewart, who obtained a "tarpan-like" horse by crossing a Shetland mare and a black Welsh pony.

A grulla, like all duns , exhibits a lighter body coat than mane and tail color, clear primitive markings (a distinctive dorsal stripe, horizontal striping on the back of the forelegs, often a transverse stripe over the withers), and the dark "dun mask" on the face. Zebra stripes are visible on the left back leg. The dun gene also produces light guard hairs in the mane and the tail.
A Heck horse