Another option for paint would be model car/airplane paint from the hobby department. Comes in a wide range of colors and is intended for use on plactic. Smaller cans too. Be sure to dissamble the cover, removing the purge button and spring. When you reassemble it, make darn sure it still moves freely, a sticking purge button is not much fun to deal with. I would also put a layer of masking tape on the threads. No need to paint them and the extra layer of paint may cause you clearance problems.
