I've got 12 girls but only one has these black spots on her comb. It hasn't been cold at all so I don't think it's frostbite. Occasionally one has had this before and it resolves on its own. It's only on the comb, not the waddles. I figured I'd see if anyone knows what it actually is.

I like to keep it on hand as well. Blue-Kote comes in both a spray and a liquid form, I currently have a small bottle of the spray because that's the only form of it our local farm store sells. To put it on a bird's comb, I like to go outside and spray some on a couple stacked paper plates, then take a small clean paintbrush and gently paint it on the bird's comb. A little Blu-Kote goes a long way.