With the light floor and tile, I think dark grey would work.

I was thinking of maybe getting large dark grey tiles and light walls. Would it look good?

yes...white tub and vanity?

I just did a small bathroom in greys. The walls are light grey ,with dark grey towels, rugs and shower curtain. Since it's a cottage we just bought, I haven't changed the white tub, toilet or sink, but I think the whole look is very crisp and clean.

The dark wood would help balance color if u have dark tiles and light walls.

If you paint grey, I would do a little lighter, but not much. If you get to pick out your own tile, and you are going to use a grey, I would include a constrasting, but matching strip that is at the same height as your backsplash. It would continue the striated effect of the cabinets, but going perpendicular.

One of our renovations was a half bath of dark gray with white pedestal and toilet, silver accents. It was beautiful and did not seem dark at all....even in the small space!