That does indeed look like frostbite, yet it's not cold enough yet in 'Bama (I'm in SW Arkansas).
The thing about frostbite is that it's a combination of things - cold and damp coop conditions that cause it.
Hmmm, trying to think of other things that could cause that sort of discoloration. Heart conditions can be one - not enough blood to the extremities, but you say you have more than one bird with this so that pretty much rules that out.
One other thing that comes to mind - fowl cholera. Some other symptoms of fowl cholera would be greenish diarrhea, high temperature, possibly swollen wattles, loss of appetite, coughing, and nasal, eye and oral discharge. It can be treated with antibiotics.
Hello bamsx4 from mee, in Winfield! Small world! Glad to have you in the forum, and a beautiful roo he is. Check for mites, and maybe worm them. This is a good time of year to do that anyway. Keep a watch, because that is a symptom of not feeling too well.