So I have had such bad luck with Sulley and his food. His wrinkles are extremely discolored -a rust color. My vet suggested I make his food for a while. So he is now eating beef and some vegetables. His stools have gotten so much better, but his wrinkles are still discolored. I clean them and have tried cornstarch/peroxide, but the stain won't go away. How long do you think it will take?