Got to be something to get it off in case they make a mistake on a job.
One of the sand-blasters I use has some "methal-ethyl bad sh#$%", and I mean BAD ! ! ! That can strip powder-coating off some materials... Ex. some time ago, I was stripping stoner shelves and for some reason, I had color coded zip-ties on the tie wire for a couple of sets/groups of shelves. Less than 5 min, the zip-ties were gone! Between 5 - 10 min later it was time to remove the shelves; they were clean!
To add to Glenn's statement, all you need to do is sand/scuff the powder-coating and spray the part(s) again with the same/different color. Be for warned, if a part has close tolerances, you may want to consider sanding those areas extra to keep the thickness to a minimum for the second coat...
Chedki - In your case, they can be sanded w/ 220 on a D/A Orbital sander and sent back for another coating with the new color!