I just used some matt black hi-temp paint from an aerosol can, you must sand the surround for the paint to key properly and take great care when disassembling the lights.
In fact you may as well send the reflectors off to be re-metallised while your at it, I use
www.zeusproducts.com.au
here in Melbourne, they make hardware for the funeral industry but they will do one off jobs.
Call Gary Scott: 0449 997 289