I'm fairly sure that he's a bay, he has black legs but there is reddish hairs mixed in as well. I've had him maybe about a month and a half, so im going to wait to decipher what colour he is, but the registration says bay (although misregistrations do happen) :)
I think it is just that the hair is thin and the skin is showing through similar to the muzzle where the hair is transitions to be finer or non-existent. It is completely normal, unless it is a weird patch caused by some sort of rubbing. In my experience, during the summer and especially in warmer climates, the fine haired areas are more likely to let the skin show.