I made a mistake and painted the ENTIRE rotor first. On my first drive, the pads wore the paint off, but it made a jagged edge where the boundary line is between the swept area and the center hat.
A better way to do it requires just putting the brakes on as is, driving on them and then pulling the wheels off. The second time i painted the rotors what i did was get black electrical tape since it will go around curves easy and mask off the area that the pad swept. I also bagged the caliper to prevent overspray and taped and bagged off anything i didn't want to get paint off. Then i gave the hat and edge of the rotor some light sprays and let it dry and repeated. I had to then take the tape and bags off, spin the rotor 180* and do the part that was under the caliper.
Sounds like a huge PITA, but it really only took me about 30-45mins each side after installing the brakes and going for a drive.
If you look in the pic, you can kinda see the edge of the rotor at the top and you'll notice it's still silver. For cleaning i just wipe brake dust off with a wet sponge by sticking my hand through the spokes.
The above pic was taken 1 YEAR after i painted my brakes.