one-eyed_jim":3lkb644k said:"Grey" MAVIC rims could be either ceramic or CD ("couche dure" - hard layer). CD rims have a uniform smooth shiny grey colour over the entire surface of the rim. Ceramic rims have a rough, dark grey coating on the brake surfaces only, and usually have a "CERAMIC" sticker. The other surfaces of a ceramic rim can be silver, black, or CD.
Ceramic rims need specific brake pads. I use Shimano's. CD rims use normal pads, but don't brake as well as plain rims until the CD layer has worn away.