My beardie will randomly puff out his beard, sometimes when sleeping or when just basking ... It doesn't turn black or anything just puffs out... sometimes for a few seconds or minutes and eventually it goes down.
He also does this random swallowing motion to, again randomly, for a few seconds/minutes and sometimes while sleeping or basking ..
Is he making any kind of noise when he does it? Or is he shedding? How often does it happen? My guy will let his puff out every so often so it's probably nothing to be too concerned about. That being said, I'd wait and get a more expert opinion. Shouldn't be anything wrong, I know sometimes they just like to stretch their beard out.