It could be food allergies. What were you feeding him before? Also dogs with white coats and less pigmented skin are more prone to skin issues. Ask the vet if it's ok to put sun screen on him when out in the sun. Though you've switched to a raw diet, you still need to pinpoint whether or not he has food allergies and what food(s) he's allergic to so that you don't give it to him in his raw diet. In most cases it's the grains or protein (chicken, duck, etc.) that cause an allergic reaction.
In my opinion the spots showing through his fur look normal, I've seen that a lot with dogs similar to his color, however his skin does look a bit red and irritated. You really need to have a vet test him for allergies.
