I resprayed mine - you can buy black bumper paint. Takes a lot of time to mask the car up & get it perfect - but it's worth it in the end. Some members use Back to Black - it's okay for a temporary fix.
if you do sand make sure you use fine grit paper like p1200 nothings worse then getting ll the scratch lines in the bumpers! if you did accidently do that rub over with fine paper then use filler primer.