BROWN can be caused by many agents.
The Silver gene can dilute Black to Brown (or even red)
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
OR, from the Animal Genetics website
Dark Bay and Dark Liver Chestnut may look brown. These effects are caused by the Sooty gene.
Photo: S M Jackson
Black horses often fade to Brown each season before they shed out to fresh Black again
RARE & MISCELLANEOUS: BRINDLE BROWN CHROME CURLIES WHITE DUN OR BUCKSKIN? CHIMERAS AND SOMATIC MUTATIONS
GENETIC OVERVIEW EQUINE BASE COLORS DOMINANT GENES DILUTION GENES RECESSIVES