this is the best definition I could find and the one that I agree with.
"Difficult to distinguish from light chestnuts but has more yellowish
body showing little or no red. Mane and tail are often same as body,
but with flaxen mane and tail, may appear similar to dark palomino."
I *think* the main difference between sorrel and chestnut is the color
of the mane and tail. Chestnuts have solid red manes/tails, the color
of their body hair (but they may have some darker hairs mixed in too).
Sorrels can have white or flaxen color in their mane/tail hair.
Sorrels are usually a little more orange than red in color.
Among the variations of sorrel are, that I remember hearing or using:
Cherry sorrel a dark deep red (Red Sonny Dee AQHA is listed as this
color) Chestnut Sorrel a dark red with lighter colored legs Light
Sorrel a strawberry blonde color (we call this orange)
On the subject of color, I disagree with the Sorrel coloring of mane/tail.
I have a dapple chestnut, with a flaxen mane/tail. Sorrels can have solid
mane/tails same color as the body, or flaxen mane/tail. Chestnut is similar
to Palamino, only darker, some people refer to her as a dark Palamino, where
as Sorrel is Red, either bright or dull, lighter shade.
I would classify the one above as a sorrel due to the lighter lower legs and slightly lighter mane and tail