No dead-giveaway lightened muzzle points to him not being a seal brown. Sun-faded black I'd say. Seal browns have a very obvious mealy or tan muzzle that stands out against the darker coat during the winter months.
But I would never consider contradicting NdAppy on this matter in any case!!
Color is very confusing. The research I did says Seal Brown has Black points. It also said Seal Bay has brown points.
Hard points are indeed black, but soft points are lighter on a seal brown.
Here's my seal brown, very typical. Black legs, black mane and tail. Brown stifle area and muzzle. Stifle area can also be lighter due to fading but the muzzle colour is always a dead giveaway as I said, and a seal brown will not necessarily be lighter in the parts you'd expect to see more sun. Faded blacks also tend to have fading on the mane and tail - which seal browns are unlikely to have.
It may be just black. There's no black that doesn't fade a little bit in the sun. I've heard of people who have breeds that come only in black (like friesians) and if they leave them too much in the sun, they are desperate because of the reddish fading. Some even dye the horses with henna so they're black-black again.