I painted the 25" TV I installed in my MAME cab.
I used Krylon for plastics paint.
I also bought some 1/4" masking tape from a hobby shop used for plastic models (cars). It's flexible, conforms well, and is easy to remove. Once I masked aroung the frame edge, I then used the wider painters tape (blue 3m I thnik) you get at a hardware store to cover the rest of the picture tube. I just applied several thin coats and the results were great! I did run an exacto around the edge before removing the tape, just to make sure I didn't accidently pull the paint off with the tape.
I'm very happy with the results.