Here's a way on how to paint a brake caliper
1.Securely jack up the vehicle.
2.Remove the tire and rim.
3.Cover entire car including wheel well with draps or newspaper and tape.
4.Clean the caliper with wire brush and cleaner solution.The cleaner the better the paint will stick.
5.Remove Caliper.Use rachet and remove the two bolts on the back side of the caliper.
6.Rest the caliper on the rotor or hang it from the wheel well with a coat hanger.Be sure not to stress the brake line.
7.Once removed clean again with brake cleaner and a tooth brush.Protect your eyes from the chemicals with goggles.
8.Mask off exposed cylinders.
9.Place caliper in a place where you can access all sides and thoroughly spray paint them.Wait 10 mins and apply 2nd coat.Wait another 10 mins and apply 3rd coat if neccesary.Paint will be completely dry in 30 mins.
10.Remove masking,reassemble brake caliper and remount wheels.