I have a mixed flock of 17. Within the past 2 weeks several of my hens have developed black coloration on their combs. I have a well ventilated coop, and though I live in a very cold climate, the coop is dry and even has 2 heat lamps that chickens can get under if they are chilled. Also, the weather from November through January was mostly below 0, sometimes as low as -20, but I had no issues whatsoever with frostbite. This black coloration coincided with the onset of unseasonably warm weather, which made me think it's not frostbite. The chickens have been rolling in a big pile of hardwood ashes, and I thought maybe it's just dirt and grime, but it doesn't seem to be coming off. The combs and waddles are effected, and even the face of a couple of hens. They don't look swollen or anything, and the chickens are not acting uncomfortable. Could this be fungus or something? Do I need to take action? I have seen this black stuff on about 6 of the hens, it started with just 2 of them about 2 weeks ago. The remainder of the flock all have healthy red combs and waddles. I have attached pictures below. Thanks for any and all help!