Hi there, skin blemishes , discloration, smudges + scratches are very normal in beardies so there's nothing at all there to worry about.
Sometimes it's even a speck of food or even poo if they have it in their tank + walk through it at some point. But that little speck is not a problem + will probably be gone soon enough. Here's a pic of a smudge on one of my beardie's beards [ years ago] , perfectly normal to see and no health problem at all even if there are a few damaged scales. They are rough little creatures that live on rocks, logs, sand + dirt !
https://www.beardeddragon.org/media/29879/full