Do you have a wire dog crate that you could place him in with his own food and water, then place it is the coop or run with the hens? I would go ahead and soak his vent area, and clean him up. My roosters with large combs in the past have changed colors like that, especially if cold, and as long as it is just the tips and rear of the comb, I wouldn't worry. When you let him out with the girls to mingle, you can get some BluKote and spray his red area to prevent pecking. Good luck on his full recovery.