This guide is written to help identify horse colors. It does not explain the genetics behind the colors. If you would like to know more about the genetics of these colors please visit Dilutions in horses
All of the dun colors, Red dun, Bay dun, Brown dun and Black Dun (Grullo) have certain characteristics in common. These include Cobwebbing (darker markings on the face that resemble a cobweb in shape), face mask (darker coloration on the face), shoulder bars, leg bars, and dorsal stripes. These markings are often referred to as “Dun Factor” markings. Although most dun horses will have at least some of these markings their intensity can vary greatly. All dun horses however, MUST have a dorsal stripe. Without a dorsal stripe the horse is not dun. The dorsal stripe should be unbroken and visible from the withers to the tail head. In many dun horses the dorsal stripe will also continue into the tail sometimes being visible it’s entire length. Sometimes a non-dun horse will have a dorsal stripe. However, this is called countershading and is not the result of Dun. Telling the difference between Dun and countershading can be difficult. The general rule is that a dun dorsal will be crisp and present all year round while a countershaded dorsal will likely have a “smudged” look and it’s intensity may vary with the seasons (to read more about the difference see Dun or Countershading). Duns will also have a diluted body color, although the amount of dilution can vary tremendously. Dun seems take “shine” away from the coat. Even very healthy dun horses will rarely have the shine that is present in other coat colors. Dun horses also seem to lack dapples and while they can be present they will be a rarity rather than the rule. In order to be dun a foal must have at least one dun parent.
This color will generally be a light chestnut with a dorsal stripe, leg bars and sometimes cobwebbing. The color can vary from a very light “peach” to a deep red. However the dorsal color should always be at least a shade darker than the body. The dorsal stripe and other dun factor markings will be red. Red dun can be present with or without a flaxen mane and tail.
Bay dun is sometimes called Zebra Dun and will be a tan or yellow color with a black mane and tail and black lower legs. They will often have less leg black than a bay horse with leg bars or mottling present behind the knees. Leg black may not be a true black but may be a brownish color that looks black from a distance. The dorsal stripe, leg bars and cobwebbing can be dark red, brown or black. A face mask, if it is present, will be the same color as the other dun factor markings although bay duns are often found without a face mask. Due to similar body color, bay dun is often confused with buckskin but the dun factor markings on a bay dun should clarify things in most cases.
Light Brown duns are difficult to distinguish from bay dun and dark Brown duns are often mistaken for Black duns, however, there are a few differences. Brown duns will almost always have a facemask and their leg black will often come above the knees whereas bay duns will often lack a face mask and will have lower leg black. Brown duns will have a darker body shade than a bay dun. If a dark brown dun is compared to a black dun (grullo), the body will be brown hues rather than gray like the black dun. It is often not necessary to differentiate between bay dun and brown dun however, brown duns mistaken for black duns can be troubling for the breeder who is trying to produce black dun foals. Often foal pics can be helpful in distinguishing brown dun from black dun (grullo) foals. Brown duns foals will most often be born a very similar color to bay dun whereas black dun foals are most often born a very distinctive beige color.
Black dun (Grullo)
Black Duns can range from a very light silver color to almost black. The light silver shade is often referred to as “Silver Grullo”. This is not technically correct as a true “Silver Grullo” would also carry Silver. It is however used as a descriptive term especially in Quarter Horses. The most common black dun coloration is the color of slate stone. Black duns will almost always have a facemask which will be black. Other dun factor markings will be black as well. A very dark black dun is sometimes called Lobo Dun and can be almost black in appearance but these are quite rare. Black dun foals are often born a beige color with or without a face mask.