My chestnut mare's tail goes from a nice red to an almost black, so I'd say it's completely possible that he could be a chestnut.. but I'm thinking he's something else. We'll have to see what the colour experts say!
Hmm it's really hard to tell from these photos unfortunately. He could be a chestnut with sooty in the mane and tail, or he could be a wild bay with pangare hiding his black points on the legs. However, I can't say either one with certainty from these pics