I believe when we were discussing the remodeling of the front license plate holder [to move it lower] someone posted a site that sold custom colored buttone to plug the holes. Sorry I don't remember the site but perhaps someone else might.
Automobile(s): 2011 CTS Premium AWD Sport Sedan w/FE5 - RadiantSilver|Ebony
Re: License plate holder front
The site is: http://www.bumperplugs.com/
I purchased a pair of their plugs for my previous CTS, an '09, and they were great. High quality paint finish -professionally done, and they were a perfect match to the car. Well worth the money.