When people refer to the colour of Porsche brakes, they are actually referring to the colour of the calipers which serve as housing for the brake pads.
Porsche calipers come in yellow, red, black and titanium; each colour has a specific significance. Black calipers are the base colour for all models, and titanium calipers are on the "Cayenne S" model.
Yellow calipers signify the special, Porsche Ceramic Composite Brakes; these brakes are optional for the "Cayman," "911" and "Boxster" models. The carbon, fine-ceramic compound of the PCCB is lighter in weight -- and more resistant to high temperatures -- than traditional iron brakes.
Red calipers signify an "S" version of a particular Porsche model. The "S" stands for "Sport," and distinguishes the Sport version of a particular model. These models feature more horsepower and higher performance than standard models.