I noticed a few small black spots on one of my pullets comb. On the side of her head, the comb looks a greenish color like it's mildewed. She spends most of her day inside the coop due to the bigger chickens picking on her. It's not too cold and the coop is dry. I turn a light on for them during afternoon. None of the other chickens seem to have this problem. She is eating and drinking without difficulty. What could this be? Thank you!