More than likely your stock brake pads are creating deposits. I experienced this after a track day with the bike and very hrd braking. The rotors turn dark purple and develop little spots on them. This is from the stock pads exceeding their performance limits. Rest assured a new set of pads and the correct break in proccedure for them will result in perfect brakes again. If you ride hard get a set of softer pads, you will be happy.