Many dun horses have dirty yellow, pale yellow, or even white strands of hair concentrated on the edges of the mane (Photo 29). Sometimes there can be so much frosting, as it is called, that the mane looks white. Although the latter scenario is rare, it can create difficulty in determining the color of the animal. Frosting is frequently dark in summer and becomes more noticeable in winter.
Frequently in addition to frosting in the mane, there is also light hair in the tail (light guard hair). It can be white or pale yellow and is located along the sides of the tail dock, concentrated at the base (see Photos 26 & 27).
Dark ear rims and white tips are present in almost all dun horses, spanning the perimeter of the ears (see Photo 29). In contrast to the bay and brown horses, this primitive marking is wider and has clearer boundaries.
When the lower part of the horse’s head, from the eyes to the nostrils, is darker than the forehead, neck, and body, he is said to have a mask (Photo 30). This is most noticeable when the horse is observed from a distance, and in bay- or black-based horses. It can be less obvious when the horse has white head markings.
Many horses have more or less noticeable darkening on the withers and shoulders in the form of a stripe or shadow (“wing”) perpendicular to the spine with poorly defined boundaries (Photo 31).
A noticeable concentration of dark hair is often found on the neck near the mane.
A ventral stripe along the horse’s underbelly resembles the dorsal stripe (see p. 22), but it runs down the middle of the abdomen parallel to the spine.
Of all the primitive markings described here, the dorsal stripe is the only one “required” for the categorization of dun color. Zebra bars on the legs are common, but they may not be always noticeable against dark background hair. The remaining markings I’ve mentioned are encountered in different combinations and can be poorly visible. The color of primitive markings varies and depends on the color of a particular horse. They are usually the color of the horse’s guard hair.
Bay Dun
Like the bay base color on its own, the Dun gene in combination with bay (bay dun) has many shades. The horse’s body color can vary from brownish red to almost yellow with light reddish or ochre tinges (Photo 32). The mane and tail and lower legs are black or sometimes dark brown. In dun horses, the tips of black hair frequently lose their color, and therefore the tail and mane can appear “rusty” due to sun exposure. Primitive markings are black or, less frequently, brown-colored. The following distribution and color of markings is most often observed: The mask is dark red or brown, and cobweb markings and any other admixture of dark hair on the body is black. The dorsal stripe and zebra bars can be either of these two colors. The hooves and skin are pigmented, the eyelashes reddish, and the eyes hazel, or sometimes light hazel or yellowish. Some horses show the pangaré trait (sometimes called “mealy”) with lighter hair along the flanks, belly, inner legs, muzzle, and around the eyes (Photo 33 and see p. 72).
It is possible to find bay dun horses with a color that is practically indistinguishable from the usual bay color. Bay dun color is the most common “Wild” color and is often seen in Quarter Horses. It is also frequently encountered in such breeds as Vyatka and Bashkir Horse, as well as other aboriginal horses. The color is rare in some breeds, such as the Andalusian and Lusitano.
Grullo
Grullo (sometimes called grulla) is a color resulting from a combination of the Dun gene with the black base (Photo 34). These horses have ashy, grayish body color, sometimes with a distinctive bluish tone. All the body hairs have the same color—a major distinction from the gray and the black roan colors (see p. 44). The mane and tail are black, and the head is dark or almost black because of either cobwebbing or a mask, which when present together are superimposed on each other. The lower part of the legs is black, or sometimes dark ashy with a tone close to the body color, just darker. Primitive markings are black. The skin and hooves are pigmented, the eyes are hazel or (rarely) light hazel.
The grullo color can be subdivided based on its shades. Dark grullos are almost black, sometimes with an inconspicuous brownish tinge on the body, while the mane, tail, head, and lower parts of legs are black. Primitive markings are difficult to observe against such a dark background, and the horse can be mistaken for black or faded black (see p. 11). This color shade is very rare. Light grullos are characterized by a pale ashy color to the body hair and black or dark ashy guard hair (Photos 35 & 36). The eyes can be dark-blue with a blue ring around the iris, especially at a very young age, and from a distance they may appear hazel. Some breeders of Quarter Horses consider this trait an indication that the horse is carrying the Cream Dilution gene.
Sometimes the body hair can have a light yellowish tone, which according to some Polish scientists studying the Konik breed, becomes stronger in winter (2004). It is true that the overall color can change its tone depending on the season, and it tends to be most noticeable in horses that live outdoors. Mares are usually lighter than stallions. Interestingly, frosting is more often observed in the mane and tail of horses with this light shade of grullo.
Grullo foals are born ashy colored. Light grullos are born yellowish or cream, and very seldomly, light reddish.
Grullo color is common in Polish Konik Horses (up to 95 percent of the breed), Quarter Horses, Vyatka, Heck, and Bashkir Horses. Occasionally it occurs in Norwegian Fjords. Light grullo color is common in Sorraia Horses, Connemara Ponies, and Yakutian Horses.
Red Dun
The body color of a red dun horse can have various shades, but as a rule it is lighter than in standard chestnut horses (Photo 37). Primitive markings are of red color. Often the head is darker than the body, showing a mask or cobwebbing. The lower legs, mane, and tail are also darker than the body. The skin and hooves are pigmented.
Dark red duns are almost indistinguishable from ordinary chestnut horses in terms of body color, but they will have noticeable primitive markings. Light red duns are almost yellow or sand color and resemble palominos (see p. 19). This color is common in the Norwegian Fjord breed (Photo 38). In 2013, Russian scientist Tatyana Zubkova found examples of light red duns in two breeds where it was not previously considered present: the Budyonny and Russian Don. Their colors were confirmed by DNA analysis.
Other Colors Determined by the Dun Gene
Besides the colors just described, there are others determined by the Dun mutation.
The combination of dun and buckskin (dunskin) results in a very light yellow or pale sandy body color with black or dark brown primitive markings (Photos 39–41).
Palomino horses carrying the Dun gene (dunalino)