What he said. You can buy nickel plated tubes or white ones from several sources. I like to paint BOTH the inside of the blank and the outside of the tube. That pretty much assures that you don't get scratches showing thru which sometimes happens if you only paint one of them.
Don't use cheap paint. It doesn't pay. Also watch out for the glue dissolving the paint leaving show thru. I like to just use the nickel plated. Simple and sweet. Make sure that you get a good even coat of glue on the tube or you will have splotches of glue that can show thru on top of the nickel or paint.
One more thing if you use CA to glue in the tubes make sure that you spray some accelerator down the inside of the blank and then work fast to spread the glue and get the tube in place. It will set FAST. If you don't do this, you will sometimes find that you'll spin a blank on the tube because the glue inside never set. The glue likes to start curing by absorbing moisture from the wood to set up but there is zero moisture inside a plastic blank unless you put it there. Accelerator replaces the natural moisture we find in the wood and helps the curing of the glue so the tube bonds to the blank.
Here is a nice discussion of CA glues.
http://www.woodturningvideosplus.com/cyanoacrylates.html
If you have time, epoxy or urethane are good alternatives for gluing in the tubes.