As for ease of cleaning in a kids' bathroom, I personally would go with a midtoned floor with midtoned grout and larger format tiles to minimize grout lines. Actually I think the lightness of the floor tile isn't as important as the grout. One of my quite fastidious friends with no kids really regrets the white grout on her white tile bathroom floor. The tile is ok to clean up but the grout shows all. I would not hesitate to choose a different (lighter) tile for the shower walls. I wouldn't paint the walls in the rest of my house gold to match the hardwood. In my powder we went with a concrete look light grey floor tile that was available in both polished and matte. The polished looked VERY different from the matte, so different that I'd hesitate to use them both in the same room. If I'm honest, the polished was the more beautiful but we went with the matte for safety's sake with the large format.

There is no real rule. You do want them to coordinate with one another in terms of relating to the overall look of the bathroom. But they can coordinate while being different materials (porcelain on the walls versus natural stone on the floor), different sizes (subways on the wall versus squares on the floor), and different patterns (running bond on the walls versus diagonal on the floor). The above is simply an example. Much of it can depend on the size of the room and the amount of tile to be used. Using the same tile everywhere in a large bathroom could look a bit too monochromatic and uninteresting. There would be no change in material or pattern to draw the eye from detail to detail as you look around the room. In modern or contemporary design that might be desirable; a slick, clean, uncluttered look. In a more traditional design it might simply be boring. Large format tile always lends itself well in modern styles. Mosaic can be implemented for a period look. Mosaic is busy given the many individual tiles, But it can be made to look "detailed and busy" by using a contrasting grout color. It can be made to look cleaner and slicker by using a grout color the same color as the tile. So there is no real right or wrong as a whole. Sometimes anything and everything can work, but often it's how it is implemented into the design. But you need a starting point. A design style, for example. Having an idea of what look you are trying to achieve will lead you through the selection process; tile material, tile color, tile size, layout pattern, grout color.

@millworkman Thanks for your response. In this case, sounds like he has to redo everything. I don't want to go through the trouble. I guess I'll just have to live with it. For waterproofing, we put paper behind hardiebacker and we taped hardiebacker joints then applied thinset. For the tub bathroom, we added one more step which was flashing the tub to the wall.

This might be good option if you're trying to stay clear of subway tiles, larger format that's not too busy but still has a nice texture and some dimension! Angela Harris Inspira Light Silver 24x48 Matte Porcelain Tile