BROWN can be caused by many agents.

This PMU foal is clearly BROWN - but what is the genetic background? Could be chocolate palomino, silver dapples, appaloosa, or smokey black

SEAL BROWN is a black horse with tan/gold mottling around the muzzle, elbow and flanks. A common explanation for this is that it is due to the action of the Pangare gene on a Black base.

Angelo, a "Wild-Type Bay" brown horse.

Recent research in France indicates that Seal brown may be caused by A+, the "Wild Bay" version of the Agouti gene, which removes eumelanin from the horse's soft parts, creating a brown effect.

So... who's right? The Jury is still out!

The Silver gene can dilute Black to Brown (or even red)

Grulla is a black diluted by the Dun gene to a soft mocha brown (with stripes and dark face)

Both The University of California at Davis and Animal Genetics, Inc. of Florida can test for the presence of Tobiano, Red, Frame, Creme, Silver, Sabino1, and Agouti (Bay). The test for Tobiano can determine whether or not a horse is homozygous of heterozygous. The red, silver, and agouti tests can help determine the agent responsible for brown coloring in an individual horse.

You can download forms for these tests from their website-- follow
the links from http://www.vgl.ucdavis.edu

OR, from the Animal Genetics website
http://www.animalgenetics.us/Equine.htm

Silver Dapple acts on a black base to create a striking effect that is often mistaken for Liver Chestnut