For almost all of the opaque acrylic blanks I use, I paint the tubes knowing that there is a good likelihood of the tube showing through. White usually helps out quite a bit, but I purchased a few other colors of spray paint and use them as needed on the tubes. I know many customers won't mind, but it always bothers me. The only time painted tubes won't help is with the very light colored blanks. For those I use white on the tubes.
Paul