My Rooster's comb has turned black at the tips. The winter here in Kansas City is really mild, no snow so far and only a handful of days below 0. Most night's are in the 10's or 20's. I can't believe that he got frostbites but what else could it be ??
It looks like what happened to my one roo. It's hard to say if he will heal or lose part of his comb. One of my roos escaped and was stuck out in the wind one afternoon. It was above freezing but the wind chill was cold enough to do damage. Two of his points turned black. They must not have been too bad because they are getting better and do not look like they will fall off. Put some salve on his comb.
I'd sure look at the ventilation in the coop. Insufficient ventilation causing increased humidity levels in the coop is usually the cause of frostbite, not the cold. That sure looks like frostbite.