I have had frostbite in a few rooster's combs in the past. It can take a week or so for you to be able to see if it it mild enought to heal, or if it is just going to dry up and round off in a few weeks. If it is opaque, that sounds fairly serious. Honestly I usually don't use anything on the combs since they are so painful, but many use plain neosporin or Vetericyn spray. You can see a lot of images of frostbite in combs if you just Google it. There is one of an opaque comb.