ABSOLUTELY paint the inside of the BLANK, not just the tubes. With a clear blank, you will see any voids in your glue if you only paint the tubes. If you are picky like me, these voids will bug the heck out of you. You will want to get good coverage too. Remember, when the blank is turned round, it acts like a magnifying glass and will make any imperfections in your paint or voids in your glue stick out.