Go to your local auto parts store and grab some brake cleaner. It is really nasty alcohol in an aerosol can. If it doesn't dissolve that paint quickly, nothing will. You should be able to wipe the paint off with a rag soon after spraying it with the Brake Spray.
This stuff is designed to wash away all the gunk that accumulates on your calipers and rotors, and evaporate clean, so as not to clog up your new brake pads.