match the grey in the tile as close as possible, err on the lighter side but not white if you can't find a real close match and after it has dried use a non color enhancing sealer on it to help keep it clean

I have installed 12" x12" ceramic floor tile, It has a white/grey pattern. I want to apply a grout that will blend in and not stand out. I want the tile to be the center of attention. What color should I use to make the grout blend in and have the tile stand out? White , light grey or darker grey? Thanks for your help