There are lots of slate tiles with those colorings. Without a picture or at least a name of the slate you have it's hard to say what it will work with it because the answer is largely dependent on which slate that you'll be using. If you have it available, you should probably just take a sample of it to the store so you can hold it up to tiles for a visual.

The slate is called "Brazilian blue/ gray" (we decided against the green tonight). It is uniform in quintessential slate gray color and nearly free of texture.

I guess I'm wondering if I can just put it with very simple ceramic tiles of whatever color looks good next to it?

Ah, ok, that's a pretty tile. I've seen applications of similar tile used with simple ceramics and it looked nice. Maybe you can incorporate some embellishments of the gray slate to the ceramic to help tie them together. This is an example of what I'm talking about. We used 1x1 mosaic tiles of black noir travertine to tie our niche to the shelf, bench, and wall feature in our shower. We also used the 1x2 mosaic on the floor, wall feature and niche. It will look nice regardless but I tend to like adding something different or unexpected.

I used a dark gray river rock tile in my last bathroom and put very simple 8" square white glossy tiles, turned on the diagonal like a quilted Chanel bag, on the walls. This time, I used the same white tile with green slate-like flooring and set them in a running bond. In both cases, there were other elements that took the spotlight -- a wall of sparkly Silestone in one and a half wall of colorful glass mosaic in the other. You could do the same with whatever accent you choose.

You can't see the floor, but it's dark blue-green and looks like slate.

I think you've got a great vision --
And a very simple white or creme tile with a modern vibe, accented by sparkly glass or something else with a bit of 'twist' would be great.

Maybe a large format 8 x 16 or 12 x 24 tile on the walls with an accent strip?

I'd go tile shopping and see what sings to you...
(Though I'd find any excuse to go tile shopping...)

I don't have a current pic but I have slate tiles in entry going down hall to laundry, guest bath and to garage door. The bath has an insert that looks like white subway but is actually fiberglass or whatever. But it looks like white tile. I have white crown molding in room. It looks very nice and actually I never even considered what the floor would look like with it because the "tile" in shower is white and neutral.

I think your floor would look great with white or even an ivory tile. But if your baseboards and trim are white I would stick with white. Then you can use whatever color to accessorize the room or pain the walls.

Ok, so I took some pics. You can see the floor and the "tiles" in shower.
{{!gwi}}

Thanks so much for the good ideas and pictures. I guess I thought of slate as having such a "look" that I was locked into having it everywhere. But I see now that the dark color goes with white, glass mosaic and smaller-detailed stone tile too. Yeah!