White subway tile is always an option. Or this one below.

grey glass subway tile

Either sleek white subway tile slightly oversized, or a neutral subway tile with a small amount of texture. There is so much visual going on with the beautiful granite, an understated backsplash may be best. Keep it light in color, especially with the grey floor.

I vote for large subway tiles in light grey or white. That granite is gorgeous by the way.

I think we are all in agreement with you that you need a new backsplash. Your granite does not want any competition. And I agree with everyone else. Either go with a solid white subway tile, or a gray color. Unless your kitchen is going to be painted red--then I would say go with black subway tile!