Grulla definition as given by the International Buckskin Horse Association: Grulla is an intense color. The body color can be mouse, blue, dove or slate colored, with dark sepia to black points. Grulla (pronounced grew-yah) has no white hairs mixed in the body hairs. Grulla horses have the dorsal and shoulder stripes, and leg barring.
Quite simply, GRULLA is a horse color. Sometimes confusing people, it is also known as GRULLO, but means the same thing. The International Buckskin Horse Association, for example, calls it grulla, whereas the American Quarter Horse Association will call the same horse grullo. Some people use Grullo as the masculine form, grulla as the feminine form. Grulla can be found in several different breeds, but is rare, when considering the total horse numbers vs. the number of grullas.
The DUN FACTOR GENE is what makes a grulla what it is. This gene is what turns a sorrel into a red dun, a bay into a dun, and a black into a grulla. So basically, a grulla is a black horse with the dun gene thrown in to produce a grulla. The dun gene is responsible for the DUN FACTOR MARKINGS one will see on a dun, red dun or grulla horse.
Dorsal stripe- a stripe from the withers down the length of the back and into the tail, which every dun, red dun and grulla horse MUST have. Some dorsal stripes will also have 'barbs' coming off the dorsal stripe.
Leg Barring- horizontal stripes on the legs
Ear tips and Ear edging- Tips of the ears (viewed from the back) are darker than the rest of the body, sometimes with stripes on the lower half, and viewed from the front, the edges of the ears will be outlined.
Shoulder stripe or shadow- Transverse stripe over the withers
Neck Shadowing or stripes- Dark areas on the neck and down to the shoulder
Cobwebbing- dark markings on the forehead, resembling a spider web
Face Masking- dark shading along the bridge of the nose, and may spread to the jaw, muzle and around the eyes.
Mane and/or Tail frosting- Light hairs in the mane or tail.
Mottling- shadowing/shading that is darker than the haircoat located on the forearm, gaskins, shoulders and/or stifle. They appear to look like 'reversed dapples', as they appear circular.
Just like any other color, grullas come in many different shades. Below are three grullas, each one being different in shade. I have actually had people pull into my driveway to ask me what color my horses are when I had several in my pasture. Not very common to see a bunch of grullas in a pasture. Non-horse people just aren't used to seeing them!