Hi Jon, as an awfully nice traffic policeman once commented about my cab callipers, painted red eh, makes it go faster does it, apparently he was one of the new breed that have to go on a course about spotting vehicle defects out on the road and told me all about it in great boring detail and when he finished I asked him about the reason why he thought I had painted my callipers, he didn't even come close so when I explained about discs becoming magnetic because of friction therefore attracting any small parts of rust that came off the calliper or disc centre and thats why the disc ends up looking like a 45 record, if they are painted no metallic debris other than what occurs naturally, all this came from a braking seminar for Lucas/ Brembo that I attended 30yrs ago, very glad they knew what they were talking about, they make the brakes.
Steve.