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) resemble light palominos (see p. 19), and their primitive markings have a rusty or dark yellow color (Photo 42). The mane and tail can be practically all white with only the middle part of the tail containing colored hair as a continuation of the dorsal stripe.
One of the rarest colors in this group is double cream dilute (Ccr/Ccr) combined with the Dun gene. Such horses have a cream body color with a pale caramel dorsal stripe and zebra bars, and also pink skin and blue eyes (sometimes called wall eyes or china eyes). Dun horses carrying one Cream Dilution gene often have light-brown eyes.
Another rarity is the smoky black plus Dun gene color (smoky grullo). Visually it is closest to light grullo color with a yellowish tone (see p. 24), but it is impossible to distinguish the two colors without DNA testing. Such horses have dirty-brown or dirty-ashy, yellowish color, lighter toward the underbelly, and the mane, tail, and lower part of the legs are dark brown (Photos 43 & 44). They have a remote resemblance to faded black (see p. 11). Foals are born an ashy color that is lighter than grullo.
These colors are all fairly rare, and when found, are often in the Norwegian Fjord, Quarter Horse, and Bashkir Horse breeds.
Inheritance of Colors Determined by the Dun Gene
The dun colors are controlled by a dominant allele of the Dun gene (abbreviated as Dn+). This allele is considered the “Wild” version of the gene, while its mutant form (nd2, which means non-dun2) in a homozygous state defines the usual, ordinary non-dun colors. The result of its action is dilution of eumelanin, resulting in bluish or ashy hair color, and pheomelanin, resulting in light red, apricot, or pale caramel. However, the mane, tail, head, and lower part of the legs are diluted to a lesser degree, which may indicate the involvement of a temperature-sensitive biochemical mechanism. An integral part of the action of the Dun allele is the manifestation of primitive markings, and these have an unclear mechanism of formation.
According to a hypothesis made by Nancy Castle (2008), primitive markings are created
