Copper tubing comes in all different shapes and sizes, and can be used for any number of purposes. Painting copper tubing is not particularly difficult, but there are a few steps in the process, as well as a few tools you can't do without.
Wipe down the tubing you plan to paint with a kerosene-dampened rag. Re-wet the rag with kerosene as needed to make sure the tubing is thoroughly cleaned. Kerosene will pick up dirt and grime from copper better than most commercially available products, and won't leave residue behind.
Allow the tubing to dry, then apply paint primer. Be sure to apply primer to all the visible surfaces you wish to paint, or the paint will not "stick" properly.
After the primer has dried, paint the tubing.
Give the tubing at least one more coat of paint after the first coat has dried. More than two coats may be needed to give the tubing that "finished" look, so be sure that each coat dries completely before adding the next coat.
When choosing a primer, look for one that is rated for use on metal. If there is no copper-rated primer, look for primers designed for use on aluminium or steel. Those will work just as well.
To prevent dry, rough skin, be sure to wash your hands after using the kerosene rag.