Smoky black

Smoky black is a hair coat color of horses in which the coat is either black or a few shades lighter than true black. Smoky black is produced by the action of a heterozygous (single copy) cream gene on an underlying black coat color. Therefore, smoky black is a member of the cream family of coat color dilutions, and found in horse populations that have other cream gene-based colors such as palomino, buckskin, perlino and cremello. All smoky blacks must have at least one parent with the cream gene, and a smoky black can be verified through DNA testing. Smoky black has been mistaken for faded black, dark bay or brown, grullo or even liver chestnut.
A smoky black horse usually appears to be a black horse and the dilution gene dilution factor is not visible. However, the coat may be somewhat more prone to fade to a brown shade if weathered or sun-bleached. Conversely, just because a black horse may fade in the sun does not necessarily prove or disprove that it is a smoky black. 
Two copies of the cream gene on a black base coat produce a smoky cream, a cream-colored horse which is visually difficult to distinguish from a perlino or cremello, but can be identified through DNA testing. 
Identification.
Smoky black foals must always have at least one parent with the cream dilute gene and at least one parent that carries the "E" extension gene associated with black coloring. This could occur one of two ways: A foal could have a smoky black parent or a buckskin parent carrying both genes within a single horse. A smoky black could also be produced by breeding one horse with only the cream dilution, such as a palomino, to a bay or black horse carrying only the extension gene, but no cream dilution. As foals, smoky blacks are typically quite silvery, and may be mistaken for grullos, especially when born with primitive countershading. Smoky black foals are sometimes born with reddish tufts of hair in their ears. However, both traits are also seen in many true black foals as well.
While it superficially resembles other coat colors, experienced horse persons often detect something "off" about the coat of an adult smoky black. The darkest shades among smoky blacks are almost indistinguishable from true black but for a slightly burnished look often chalked up to sun bleaching. The palest can be mistaken for dull bays or liver chestnuts, especially if exposed to the elements. Smoky black coats tend to react strongly to sun and sweat, and many smoky blacks turn to a chocolate color with particularly reddish manes and tails. Bleaching due to the elements means that the legs retain their color better, and can take on an appearance of having dark points like a bay horse. Smoky blacks, however, will lack rich red tones in the coat, instead favoring chocolate and orange tones.
One way to visually identify some smoky blacks are by the eyes, which may be amber even at adulthood. However, it is sometimes difficult to distinguish an amber-brown eye from an ordinary dark brown eye unless there are other horses available for direct comparison. 
Genetic identification.
Genetically, smoky blacks are black horses heterozygous for the cream gene. The mutation that produces the cream colors is on the "MATP gene" on equine chromosome 21 (ECA21), and is an incomplete dominant trait. Incomplete dominant traits differ from recessive traits, which are only "visible" in the homozygous state, and simple dominant traits, which look just the same in the homozygous and heterozygous states. Instead, the MATP mutation is visible the heterozygous state, but more so in the homozygous state. The difficulty in identifying smoky blacks has led some to describe black as "masking" cream, however smoky blacks are more properly termed "cryptic creams."
The location of the cream gene was published in 2003 and there now exists a DNA test for the cream gene. This test enables breeders to identify cryptic creams such as smoky blacks, dark palominos and buckskins, and creams whose coats are obscured by the action of the gray gene or pattern genes such as pinto.