All three of those breeds have much longer and heavier coats than your puppy. I think there must be predominantly something else in the mix for him to have such a short coat. I've never seen any in that colour mix either, though maybe close. And his head shape and ear set doesn't match any of the three.
Maybe some terrier in there? JR? A bit of Basenji? They would probably be smaller though.
Did you see his parents? Where did you get him? He looks alert and happy, that's the main thing. It's hard to say how much bigger he'll get but dogs have most of their height at 6 months. You will have to post back when he's a year and more fully grown so we can see and guess again.
