I'm a TOTALLY NEWBIE, so don't take my advice: LOL
I will mention two situations I have read/been told about:
1) in order to clean the dried poop/vent plug situation, it suggested putting the bottom of a chick (not the whole chick, just her bum) in warm water and then gently blowing dry with a hair dryer.
2) the woman who works at my local gym was telling me she walked into the bathroom to find her 6 year old daughter giving one of their new baby chicks a bath in the bathroom sink...she was a vet tech before she had children and she was certain the chick would die...she blew it dry and prepared for it to most likely not make it, but it was peeping around a few hours later...and ended up living...
SOOOOOOOOOOO with that knowledge I would guess you could try to gently wipe with a cloth, maybe get a little wetter, but sounds like blowing them dry is the key to keeping them warm and quickly getting them back to their normal temp.
although if it's just feather color that is bugg'n and not a health issue, I'd try to leave'm alone and just wait it out...
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AGAIN disclosure~ I haven't even gotten my chicks yet, so I'm totally new and can't really give any valid advice...sorry!