This page has been sourced from REC.EQUESTRIAN, the body of the text has been unaltered as far as possible. The information is for use at own risk.
2. CHESTNUT VS. SORREL
Sorrel and chestnut both generally refer to the same color, a reddish coat with non-black points (mane, tail, legs, ears). Chestnut is the English term, while sorrel originated in the west as the cowboy term. Both terms are still in use, with different breed associations referring to the lighter reds differently than the darker reds, but to complicate things different breed associations do not agree as to what term shall cover what shade of color.
In some breeds, such as the TB, Arabian, Morgan, and Suffolk, all shades of red are classifed as "chestnut". There are further gradations. For instance, the Suffolk has seven shades of chestnut: yellow, light, copper, gold, red, dark, and liver. The Canadian has four shades: clear, golden, dark, and burnt. The usual approach with many draft breeds is to go by the number of easily distinguished shades of red or lighter color on the horse- -two or fewer being a chestnut and three or more a sorrel. The Belgian registry uses sorrel for light yellow with pale points (blond sorrels; genetically eeffP-, flaxen-maned chestnut with pangare effect), and chestnut for all other red & yellow shades.
In the American Quarter Horse, definitions have changed. In the past the AQHA has called sorrel a dark clear red body color with no smuttiness (caused by the Sty smutty gene), and chestnut those horses that are either light clear chestnuts, or those that are obviously smutty, such as muddy chestnuts, liver chestnuts and the like. More recently they have used "sorrel" for light clear yellows and reds, "chestnut" for medium reds, and "liver chestnut" for dark reds. Their current description differs from past ones as the new directive on buckskin vs. dun will change things for those horses of those colors in the future. I have heard that the AQHA seems to have the further distinction that sorrels have lighter colored legs than the body, while chestnuts have legs the same color as the body.
Generally, when both "chestnut" and "sorrel" are used, "chestnut" is restricted to darker reds and "sorrel" to light, clear reds. Any chestnut or sorrel can have a mane and tail that are dark (tostado), medium (alazan), or flaxen (ruano). However, flaxen manes and tails are more common in horses with lighter colored bodies. Typical color definitions are given below. (From _Horse Color_ and _The Horse_)
Dun horses can have similar body and point colors as chestnuts and sorrels (especially red duns), but duns typically have dorsal stripes. Horses lighter than blond sorrel can be yellow or claybank duns (including palomino), perlinos and cremellos, and finally whites and aged greys.
(For information about the genetic terms, see the GENETICS FAQ.)
The Canadian Horse Breeders Association uses these terms: