Seal brown is a hair coat color of horses characterized by a near-black body color; with black points, the mane, tail and legs; but also reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle.

Like bay, the seal brown color lacks the non-agouti mutation that would create a fully black horse.

However, true seal browns have black points characteristic of all bay horses, while liver chestnuts do not.

[6] Seal brown is best described as a black or nearly-black coat with reddish or tan hairs on the "soft parts": the muzzle, eyes, inner ears, underbelly, behind the elbow, and in front of the stifle.

The term "seal brown" is unlikely to be part of a novice's repertoire and is therefore preferable when discussing this specific coat color.

[3] An early version of the currently-accepted equine Agouti gene theory was first presented in 1951 by Miguel Odriozola in A los colores del caballo, subsequently reviewed by William Ernest Castle in Genetics.

The trait is characterized by pale hairs, typically off-white to light tan, around the eyes, muzzle, and underside of the body.

In humans, mutations in the TYRP1 gene account for variations in "normal" skin, hair and eye coloration, as well as types of clinical Albinism.

[25] The phenotypes associated with TYRP1 mutations are typically rufous or chocolate rather than the black-dominated coats of seal brown horses, and usually result in pinkish-brown skin and light eyes.

Many black horses fade, sunbleach, or otherwise undergo a lightening of their coat color with exposure to sunlight and sweat.

A sooty coat exhibits a mixing of black or darker hairs more concentrated on the dorsal aspect (top) of the animal, and less prevalent on the underparts.

The difference between the top-down distribution of the sooty trait and the lighter soft areas of a seal brown can also be difficult to distinguish from one another.

The team of French researchers who developed the DNA test for the recessive a allele also discussed the possibility that Extension might be dosage-dependent.

The authors acknowledged that other factors could play a role, and that the claim needed to be studied on a greater scale.