It can either look really dramatic or too dark, depending on the size of the room as well as your other components. I've attached a couple of images of our work using dark tiles, the smaller bathroom we have surrounded the bath with dark tiles but then balance it with an extra large mirror to bounce the light around the room. The larger bathroom we have taken the floor colour way onto the wall but used a different texture on the walls for drama. Hopefully this gives you more of an idea but you shouldn't to nervous of the room being dark, it's where you can create a contrast as well as textures. Look forward to seeing what you go with in the end.

yes to all, we did have the tiles professionally sealed, but sealing is not a cure all in my experience but I'm sure it helps considerable . my wife does buy those hand made goats milk styles soaps etc and I don't imagine there is anything more testing for stone, and yes it does mark. The Grey ( bane of my existence )granite much more so than the beige travertine ) I must admit though, the kids bathroom was almost non existent as one has sensitive skin and uses pump pack. I would also imagine climate, airing/ sunlight, volume of use and the time you have to manage it would also be contributing factors. We are way short on time and they don't get the attention they deserve, so I would suggest asking around, others may manage it better and it not be an issue. If your only doing your bathroom you may consider the risk factor not worth it for the volume, but for me, the advantage of travertine in the rest of the house far out weighs any marking issue in the showers, and wont stop me from using it again. To be honest when we sold the last house I just took to the shower with one of those paint scrapers with the razor in the end and most of it came off and it didn't detract from the look of the house. Sorry i have probably only muddied the waters even more, good luck with it.

I am just wondering whether it is a good thing or not to go with solid colours like the dark blue (prussian blue), grey floors and white on other walls all in tiles. I see that a lot of designers seem to do a pattern on one wall, but I haven't found one suitable and whatever I do, I just don't want it to look out of date in 5 years time. I am not sure how about much of the prussian blue tile is appropriate in order for it to be noticeable but not too overpowering.

The size of floor tile: 300 x 300 mm and the size of wall tile: 300 x 600mm The floor tile and wall tile do not align at all. It looks unprofessional. Should the tiler redo the job? Thanks for your advice.