Same here. I just drybrush where the black paint wears off showing the resin. I also paint inside the imprinted lettering on my E-11, in silver, as it makes it look more real because you can see it was taken off of a real mag.
For slings however on BFG’s I muddy them up with shoe blacker, as I an imagine oil and dirt getting caught in the fabric.
But yes keep ya gun clean as possible so ya don’t get blockages