I really think it is a personal preference, and you can't go wrong. I think a gray or tan would be nice. It would still give you some depth but would not be over-powering. However, since you have dark cabinets, you could go darker.

Hope these pictures help. What do you want to be your focal point in the kitchen? The tiles, the cabinets, or the granite? Some things to consider.

Dark grout

Kitchens · More Info

gray grout

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light grout

Jill · More Info

Looking again at your picture, your cabinets are modern, so I would go for a lighter grout color. This way, your tiles will not be over-powering. Instead, you will keep a sleek look in your kitchen as it is now. Your counters have tan in them...How about a light brown/tan grout? Looks beautiful so far.

I agree on the lighter grout color. It will look much more sophisticated with a grout that matches the tile. Good luck.