Not sure whether paint would 'stick' or not.  Maybe some of the paint that they use on car bumpers 'might' work, but the 'livestock' environment is a bit harsh for any paint to withstand, especially when you add constant moisture and the abrasion forces on the paint from the cattle.

Both of the waterers I've got had the tops go bad.  Faded to a light pink before they cracked, but once cracked, they soaked up the insulation -- which froze in the winter = frozen waterer.   The yellow tank part has held up real well, one is close to 20 years old I think, the other is definitely 15 years old (date is in concrete).