NFPA 13 2010 6.2.6.1.1 LISTED corrosion-resistant sprinklers shall be installed in locations where chemicals, moisture, or other corrosive vapors sufficient to cause corrosion of such devices exists.
A6.2.6.1.1 Examples of such locations include the following:
(22)Area over and around swimming pools, chlorine storage rooms and pool pumo rooms.
I do not believe white painted sprinks are listed for corrosion resistance. However, I've gone after and been granted a variance before to do just that when it was an extremeley small pool room (10 heads, if memory serves me correctly).
By the book, I think you're looking at wax coated or lead.