I am using Style Selections Mitte White 12x24 porcelain tiles from Lowes. It is off white and quite nice elegant looking.

I like hand glazing where there is a depth of color from subtle, uneven pooling of color, In kind of a soft water color effect. I, too, like neutrals and think they are calm and simple for an elegant effect. Tone on tone is elegant, imo. Also very soothing for a retreat bath.

If you like the marble or limestone look, we were impressed with the tile from Ilva (an Argentine company, I believe). Their US division is called Crossville Tile and Stone. We don't normally like tile that tries to look like something else, but they produce a porcelain tile made in a way that looks remarkably like polished travertine, in various neutral shades. I was told it uses a "slurry" of stone products that goes into the substrate of the tile, as opposed to a design that lies on the surface. We used a gray version of it for a guest bath, and our contractors and guests have remarked on how subtle and natural it looks. I've attached a few photos.