I didn't read through all the replies, so sorry if I'm repeating what's already been said, but he looks a lot like a sooty chestnut to me. Sooty darkens colors (which would explain the dark mane and tail), and it tends to put gray or silver in the mane and tail (which I see a hint of in the bottom of his tail).
I sincerely doubt he's bay or black of any sort because his mane, tail, and knees are too brown.
He's definitely not palomino. Even with the darkening from the sooty gene, a palomino could never be that dark.
Also, I don't know if you know this, but he's definitely a sabino. White on the lower lip, blue eyes, large face markings, and jagged leg markings are all characteristics of sabino. The white on the lower lip is a dead giveaway.