Grout color is so important when making a mosaic. I almost always use a dark colored grout as I feel it ties everything together and outlines specific features. Pictured below are two photos of the same mosaic, I grouted in a gray color first and was disappointed. Today I regrouted in a charcoal black. I am very happy with it now, it's just as I envisioned!
I am a stained glass mosaic artist from Maine.