The Nissin calipers on my 650 are painted with an engine enamel paint. I did that three or four years ago, and they have held up pretty well.
2007 Kawasaki EX650 street/track 636 forks - Hyperpro shock - Woodcraft - LeoVince - Dynojet
2003 Yamaha R6 race/track Ohlins - Arata - Vortex - Woodcraft - Dynojet
OMRRA Expert # 440