Brake rotors are slowed down by the brake shoes that press outward or inward based on type of vehicle. The rotors can sometimes warp or in some cases turn a dark blue, indicating a serious braking system problem.
Basic Cause of a Rotor Turning Blue
Excessive heat will turn a typical brake rotor blue. A blue rotor indicates the rotor is being worn and could lead to cracks in the rotor, which will cause uneven wear on the brake pads that are stopping the vehicle. This uneven wear could lead to damaged calipers and brake shoes.
What Causes the Heat?
The excessive heat needed to turn brake rotors blue would require one to "ride" the brakes -- to literally be operating the vehicle with one foot on the brake. In cities where the layout is very hilly, San Francisco for example, or mountainous areas, a constant applied pressure to the brakes would cause the problem.
Incorrectly aligned calipers or incorrectly installed brake pads could also cause the rotor to turn blue. The brake pads would constantly be applying slight pressure to the pads even when not braking.
Solution to Blue Brake Rotors
Have a professional examine your rotors and determine the solution to the problem. Some mechanics suggest replacing the brake pads with ceramic pads; others recommend replacing the rotors with drilled or slotted rotors instead of the solid piece to dissipate the heat.