My ROA is bright all the way through, but my P-H Musketoon is black. Not sure why that should be so, since both are cleaned most assiduously after shooting - as soo as practical. What I do is to immediately sway out with baby-wipes to get most of the crud off before leaving the firing point.
I'll ax some more knowish folks than me on another forum, and see what answers we get.
tac