He fits some of the criteria but not all of it. So.... opinions?
^^ The flash washed alot of them out, but he has a lot of white hairs flecked through his coat.
His white markings don't have a defined edge, but blend into the rest of his coat.
He has a lot of white hairs on his hinds, above his socks.
BUT... sabino's typically have stockings, not socks, large face markings like a wide blaze or a bald face, and usually splashes of white on their belly, right?
So what does everyone think? It doesn't matter to me either way, I love him to bits, it's just something I'm curious about.
Oh, another thing I noticed was that the skin beneath his white stripe is grey, it's only pink in a couple of spots.
Here's a full body shot for a ref.
I'm currently inclined to think he's just a plain old chestnut, but just thought I'd put it out there. :)