I would think that something in the cream / tan range would look nice. You don't want something too white - it would look stark. But you also don't want the grout to blend too much with the tile color, as it would hide the pattern.

I suggest a color that matches the glass tile but is around 50% lighter in shade - that way you pick up the tile color, accentuate the tile shape, but the grout won't be so pronounced and not too light either - Good Luck!

Please tell me what you think ? A DIY job.