Originally Posted by Celeste
In my area, a brown (all shades of brown whether red or true brown) horse with black points is a bay. Apparently it depends on the breed whether you call it bay or brown.
Terms could also be different in different locations. http://en.wikipedia.org/wiki/Bay_(horse
"Some breed registries (including the Jockey Club Thoroughbred
registry) use the term "brown" to describe dark bays."
While this used to be the case, since using the term 'brown' went out of fashion, as Quixotic said, they have now isolated the gene that causes brown. On a genetic level, the horse is different. It is no longer a location thing, like sorrel and chestnut still is. Sorrel and chestnut are genetically the same - bay and brown are not.