Re: Pictures of the "chestnut" stallion.
He is DEFINITELY a bay. Registration papers can be incorrect (which is not a good thing but it happens); I'm surprised they are THAT incorrect. It could be that they sent in the registration papers really early when he still had "baby fuzz" on his legs which may have hidden the black. Still it's a pretty big error...
Anyway chestnuts will never have black legs or black "points" (mane, tail, ear lining, etc). They can be a really dark brown and less red (liver chestnuts, etc), but not black. This horse has all the classic agouti (bay) markings and even has a darker tone to his barrel (dark bay). He definitely has one black gene (and since one of his foals was a chestnut we know he only has one black gene and one chestnut gene (is heterozygous black)).