Spray enamel and Ceramcoat brand acrylic, and Testor's model enamel are the ones most often cited here. I have recently been using the Ceramcoat paints and having good results, particularly with the "pearl" colors for really transparent blanks. I don't see the need to paint the tubes, just the inside of the blank. I use a QueTip to apply the paint, and do two coats, let dry overnight. I use 5 minute epoxy to glue tubes. If you do a search using "painting" as a key word, you will find more threads about this. If you have a Michael's craft store in your location, you can get the Ceramcoat there, couple dollars plus some change for a bottle. Copper pearl works great with Exotc's Ancient Mars, or Golden Dawn.
Dan