Every winter, even though my chickens are in a somewhat warm coop, both my roosters get some black scabbing on their combs. I've tried putting neosporin on it (which is just vaseline with some medication), it's always too late and I have found it impossible to put it on preventatively. What happens is that the black part falls off and the comb reshapes itself. It has never been a problem as far as long term damage. If you can put something on the comb, then great.
Check your coop to see if there are areas where cold air can get in. Your chicken might be roosting near that opening (it could be just a pinhole). We use pieces of cardboard box cut to size for those small openings. Those patches really work well.
