I'm keeping the window white but adjusting the splash back so the window frame on the left can go all the way down to the vanity. Was planning to keep it white with a white sheer curtain, thought it would be a nice contrast. Yes I'm painting myself. Would have been easier to do between demolishing and putting in new vanity but can't decide yet so I'll wait and then maybe just start with the middle feature wall painted and see if more is needed.

I would have thought the intent of mosaic feature was to highlight a feature by drawing your attention to it. I assume the bath and window is intended to be a feature, so why not tile above bath & around window to draw attention to that.

Sounds like a very stressful situation! If there is absolutely no way the builder will allow you to change things (even if they did, I imagine they would ask you to foot the entire bill of pulling the tiles down and replacing all water proofing in addition to new tiles), I can make a few suggestions for improvement. Firstly I would suggest replacing the tiles above the vanity with a white mosaic, a patterned or a textured feature tile/strip. You could also use this same tile to replace the vertical feature in the shower. There are some beautiful shapes and sizes available to choose from. Secondly I would address the grout situation in this way: Floor - dark colour grout & Walls - Light colour grout. Lastly if it does not prove too difficult or expensive, maybe replace the tiles below the vanity with a plain white tile (could be similar size). Good luck and I am sure once you have a lovely mirror up and some crisp white towels, it will look just wonderful.

I'd embrace them, they're in good nick and terracotta has just become fashionable again. Think all the details like indoor plants in macrame plant holders - for a long time considered hideous but now completely boho chic. Better to work with rather than against your foundations. Look for images on pinterest rather than houzz as they'll be more likely to feature this kind of style.