I've noticed the same thing on my girls from time to time, just on the tips of their combs. Never all birds at once, just one or two occasionally. I've never seen any ill effects, as the coloration goes away within a day. I assume something smudged on their comb with mine. The little clowns get into so much. I have a RIR that has mud from beak to breast every rain shower. Ahh, Ruffles... you are something else. I keep an eye on them when I see it, just to make sure it may not be a circulation problem (I thought I remember reading something about blue combs at one time or another). Now that you mention it though, why wouldn't a comb be able to be bruised? They seem to make great "handles" to move other birds when getting a spot on the roost at night. If she's acting fine, her comb is upright and not flopped over (unless she has a floppy comb), and she's acting as she normally does (eatin and poopin), I'd venture to say she's alright. It's definitely not frostbite season.
