Originally Posted by Snookeys
Hm see, I was always led to believe SORREL was the lighter red color, and chestnut was darker. I always thought there was a difference, and recognized chestnut and sorrel as two different colors.
As it has been said, genetically they are the same, just two different shades of "red."
Sorrel is a western horse term, mainly used by QH and Paint Horse people. You won't find it used in the "English" breed world, Arabians, TBs, Warmbloods, etc.
Good article: Horses - horses and ponies on the internet