I would try to pick a medium tone to the blank, but that's just me. I find when I reverse paint with lighter colors, it changes the constant color of the blank from thin areas to thicker areas. I like to try and keep the constant color and not to show the inner paint color showing through the thin areas. Also, if your tubes are a little loose, reverse paint the hole and paint the tubes. That will help take up some of the slack. When I drill cebloplast, I start with a bit about a quarter inch smaller than the finished hole and drill a pilot hole, then step up to the finished size. It doesn't get as hot on the second drilling and if you melt some in the first hole, its still smaller than what you need and not ruined. I'm sure you will get plenty of advice from others on this also. Good luck!