I would do one that blends with the floor tile color. It does not appear that any of them do.

Or, if they do, it is hard to determine. I agree to find a grout that matches the floor tile color.

darker and grayer for the floor/..... light smoke, or mocha. I would do light pewter or summer wheat, but I would be sure to not be scrubbing grout on floors and they look good with the stainless, etc.

I would go one shade darker than the floor tile. You need to compare it to the floor tile, not your countertop. Have you looked at different brands of grout?

a color that matches the tile... i would not go darker, all u will see is the grout lines and that will take away from the rest of kitchen. your floor is not your focal point, it should be "in the background".