Dark areas on the comb can be indicative of a few things. First, has he been exposed to any low temps? Mild cases of frost bite can show up as darkened areas on the comb and wattles. If not, then the next reason for darkened areas on the comb is a heart or circulatory problem. Unfortunately, there's not much that can be done about that. If he has either of those going on the best you can do for him is to keep him comfortable until he recovers or passes.
Is a trip to a vet out of the question? He may have an infection, but what would you use for an antibiotic? And to treat what? Without more symptoms to work from, it's difficult to know what could be wrong with him. A bad infection will lead to system shut down and organ failure which would account for the darkened areas on his comb and the fever.
Sorry I can't be more help.