When I had the brass to paint.......
Wash completely, remove "brass" color with laquer thinner in an ultrasonic cleaner, clean with an air booth, light grit if necessary (then back in the ultrasonic), then prime and paint with thinned paint. I used automotive gloss black cause it was free (friend filled my Ragu jars at work), later a little grimy black floquil if desired. If you have multi colors just mask and proceed.