Paint or plasti dip
Most likely they are painted. Another option...Electrical Tape. I used ET to cover the Chrome Bumper inserts on my Black Caprice bumpers.There is black tape on the center pillar between the doors on my 93 RMS, and it's bubbling and coming off so I started peeling it off completely.
What's the best way to make them black again? Paint them or tape them. Anyone else had this problem?