Yes. There is a difference. I used to think Sorrel was the western description and chestnut was for english! I argued with an old-timer forever and he finally asked the vet. I was proven wrong! LOL... (the argument started because I thought my horse was a chestnut). He's a deep red w/ a matching mane. I believe the chestnut has lighter tips.
I've always thought it was a western term. I had to look it up, and to be honest I didn't find an actual answer. I think it's still a matter of whom you ask and what their opinion is. Every single color out there had a description, but when it came to those two, no clear description or answer came up for it. Below is the best answer I was able to find online:
If your horse is a Thoroughbred, there is no difference. The Jockey Club doesn't recognize the existance of the color "sorrel," all Thoroughbreds that are red and not bay are registered as chestnut. If your horse is an Arabian, there is no difference. The International Arabian Horse Association doesn't recognize "sorrel" either, all Arabians that are red and not bay are registered as chestnut. Ditto for Morgan horses, Saddlebred horses, and Standardbred horses.
So the only breed registry for which there is a distinction between "sorrel" and "chestnut" is the Quarter Horse.
At the AQHA website, you can download a free chart with the colors and markings on it: http://americashorsedaily.com/horse-colo…
The chart states that Sorrel is: "Body color reddish or copper-red; mane and tail usually same color as body, but may be flaxen; may have dorsal stripe."
Chestnut is: "Body color dark red or brownish red, mane and tail usually dark red or brownish red, but may be flaxen. Mane and tail may appear black, but lower legs will be red; may have dorsal stripe."
Now I know from experience, because I've seen it happen when we were doing the registration papers for a bunch of Quarter Horse foals, that there will be some horses where people will not agree whether the foal is actually "sorrel" or "chestnut." I've also observed that when you offer people the chance to identify a bunch of horses as either chestnut or sorrel, if you run enough horses past them, you can repeat the exercise a couple of days later and the same person will change their mind about some horses.
For me, I have never understood why it makes such a huge difference to some people to call a horse "chestnut" or "sorrel." The breeds I'm most familiar with are Thoroughbreds and Arabians, and I am very happy to not make distinctions between "sorrel" and "chestnut." I like to use descriptors to characterize the color: e.g, a red chestnut, a liver chestnut, a red chestnut with flaxen mane and tail, a brown chestnut, and so forth. Works for me.
However, there are some people that are extremely sensitive about whether their horse is "sorrel" or "chestnut." If that's how they feel, I'm fine with going along with whatever they choose to call their horse, I'm not going to argue.
Since the distinction is in some cases very much a matter of judgement and opinion, if I were you, I wouldn't argue about it with someone. IMO, arguing about whether a horse is chestnut or sorrel is "much ado about nothing."