I would use those same tiles for the shower walls and a small tile in the same gray for the floor then you could do a carrara look quartz for the counter

Sounds dramatic! I wonder if the bathroom would feel very dark with the very dark grey on floor and walls?

How about a very pale green? it would go nicely with white and dark gray and a herringbone pattern would bring some interest in. If doing the whole wall seems daunting or expensive, the dark gray you've used on the floor could anchor it on the top and bottom with a section of the herringbone in the middle. This same company has a herringbone in this color.

12.2"x12" Light Green Penny Round Porcelain Mosaics · More Info

TMK, do you have any details about the tile so that we can try and locate it? It looks very nice.

I am doing a very large master bath redo w/a 7X4 shower. Took me months to decide on tile. because I plan on doing a "plant wall w/teak shelves" on the very back wall, I'm using cement tiles like this:

but you could do it on the floor like this one:

they come in different colors and designs. For the other part of the wall I'm doing a white subway in a larger size in a herringbone. My floor will be black marble, 3" hex.

Take a look at some of my idea books on "new bathroom".

Also, take a look at Fireclay Tile. They have some beautiful choices. This was one I loved:

there are all different ways to lay subway. You could do a combo of your floor tile and then do some subway or even pebble tile.

The white subway tile has been so overdone, I agree you should go with something else. What about a larger white tile combined with the gray?

or you could do Meran Blanc Amalfi Marble. You can find it at The Tile Shop.

Thanks so much for all these great ideas!