He's gorgeous whatever! I can't see his legs well enough to see if he has black points so can't tell if he's bay or not, but I believe primitive bays don't have black points, although I don't know if they would be as dark as that anyway.
I find it really interesting what you say about his foal colour - in my extremely limited experience of foals I've seen a couple of blacks and both were born a much lighter, almost beige, colour and moulted out to black when they lost their foal coat. The only bay I've seen was also born a much paler colour (they thought she was going to be buckskin) and moulted out to bay.
Will be really interested to find out what he is! Love the horse in your avatar too.