Disc is heat-treated before machining to minimize the rotor from warping during the extreme heat cycles.
Rotor hat and disc surfaces are treated/coated by EDP with Black Paint, so all the internal cooling vanes, corners, and crevices are penetrated with a uniform coat, unlike spray painting or plating which can only reach to the external surfaces.
With only a few stops the black paint where the pads in contact, will disappear and show in metallic finish while the rest surface / area remain protected from corrosion, so the rotor will have a nice look for the rest of life w/o undesirable rusty area like OE or others.
Rotor you received:
After a few hard stops:
See the complete review here (Corvette ZR1 CCB to iron rotor conversion)