Since we moved in, this has been the bane of my existence:
Ugh...so royal blue and so fake marble. Dave and I planned from day one to replace this with nice travertine or black slate tile and build a different mantel. However, other projects were higher priorities and when we sat down a few weeks ago to project out our future renovation plans, we realized it would probably be a year before we started on any living room construction projects. Something had to be done about the blue. It was preventing us from being able to do any decorating in the living room because it clashed so badly with everything and nothing looked good in the space. We did a little online research on how to paint fiberglass and started the project. I used 220 grit sandpaper to rough up the surface and then primed it with a latex primer. I used some black semi-gloss latex paint left over from our kitchen cabinets to cover it. It's definitely much improved and will do until we get around to tiling.