A few ideas
http://elcova.com/eve/ubb.x/a/tpc/f/6706011751/m/2911055711.
I used Performix Plasti Dip (got it at Home Depot). It's been on the license brow a few months and is holding up well. Not sure how it would do on a facing, flat surface like mirror caps.
BTW, the mirror caps are pretty easy to swap. You might post a message in the classified section to see if anyone with black wants to trade for chrome. Others here have done that.