Darell,
I’ve never had any issues painting tubes and these pens sell very well. I’ve had success with a couple of different methods. The first step, just like with gluing-sand the tube a little before painting. Don’t sand it after it’s painted. It helps the paint to adhere to the tube. I used to use spray paint-krylon. This can be applied in very thin uniform coats. I’ve stopped using spray paint though because of the smell. Lately I’ve been using Testor’s Model Acrylic Paint and really like it. Other acrylics would work as well. It dries fast, but give it some extra time to “cure”. There’s no smell, water clean up, and easily brushes on in a thin coat. When I’m dealing with acrylics I also don’t use CA glue to glue the tube. I’ve been using Loctite’s Sumo Glue. It’s similar to Gorilla glue but dries A LOT faster and doesn’t make any where near the mess. I coat the tube with glue, mist it with water from a spray bottle and insert. Or I’d use some 5 minute epoxy. The urethane glues and epoxies are not as brittle as CA and doesn’t break down the paint like CA will. CA is a little better with wood since it can “soak” in, it can’t with the acrylics.
If you don’t want to paint the tube, you could also use a Q tip to paint the hole. I’ve done it either way, or both ways on the some highly transparent blanks and never had an issue with tubes not fitting.
Just remember, use enough to do the job, but not too thick.
Hope that helps.
-- Greg H.-Chaseburg, WI. www.greghaugenwoodturning.com