had the same question myself, and resolved it by installing dark wood vanities against very dark/black navy tile floors in one bath, and lighter gray in another -- both are small baths, 5x10 and 5x8. I also replaced my 5 foot vanity w/a four foot vanity, and lifted both off the floor -- lighter tops. Light walls-- white fixtures. So the only dark elements are the vanities and the floors. I liked the contrast between darks areas and light areas, but if you want the walls to carry color, continue that color into the vanities, either lighter or darker, just not the same. In the smaller bath, I used a metal frame (dark bronze) for the mirror, and for the larger bath, brushed stainless, like the fixtures. Yes, you can have too much dark, but it just depends on the walls.

I would at least go several shades lighter than your floor.

Absolutely do it like the floor. We are sure that they will be great combine for your bathroom. Check this sample;

By the way you can use black marble slab for your wall(above your vanity) and also a mirror would be great with that.

For black countertop we advise you to check for nero marquina black marble.

We have slabs of it and can make a custom fabrication countertop for your bathroom. If you wish, check our different kind of nero marquina black marble tiles.

Thank you everyone for your helpful comments. The counter and upper cabinets were installed yesterday. (Photo below) Wish I can say it's very clear now. White seems safe and will look nice. But I'm really drawn to a gray and particularly a dark one. mathomson5 your baths are about this size so it's nice to hear dark vanity and floors works for you. Emily, you photos helped. While I can see the vanity being dark, the upper medicine cabinets don't feel right being dark, but would may look strange painted the white color on the walls. Now, if my husband agreed to do the painting (he's declined), I would take the risk. But, it will be a more costly spay lacquer that will be not easily be changed.

That's a tough one! I agree that dark gray would be too much for the medicine cabinets. If you went white for both vanity and medicine cabinets, could you go gray on the walls? or do the walls need to stay white? Also, what kind of mirror will be installed? Will it span the entire space between the medicine cabinets? Is the shower already done? I'm wondering what that mirror will reflect:) Sorry, question overload!

Emily, thank you for your response. These are all great questions and I'm struggling with the answers. The shower is done and is also marble (tile rather than stone) with double doors. I planned on hanging an interesting mirror between the sconces, but now am contemplating something larger, perhaps going to the ceiling and between the medicine cabinets. Also, the medicine cabinet doors are mirrored. So the only painted will be the side and top molding. I like the idea of a white bath, but maybe gray walls will do the trick. I'm off to the paint store today to pick up samples. Doing my kitchen was so much easier for me. thanks again for your thoughts. It's been helpful.