Usually, I just brush them off. The laser leaves a really fine dust of black paint/ash/smutz that will smear really easily if any moisture hits it. I think the key to getting better color is more about thickness of the paint layer and dialing in the laser.
I want to play with some dyes too, just to see if having something soak into the fiber makes a difference.
Very cool! Are you using vary power or dots? It looks like the lighter colors burn away easier, which is what I am seeing with paints too. I need to play with those too.