Jonathandb1972, I was thinking of going with a grout that is the same colour or lighter than the grey tile. The hex will be grouted in a medium grey. This has already been done in the loo (the hex) and looks great. Neither are grouted in the above picture. Do you think there will still be issues with where the grout lines are if they are the same or lighter than the tile? Also, where the hex tile in the shower meets the grey tile will mainly be covered by the shower's profile. However, the shower only goes up to about 2m, so there will still be a visible "meeting" of tiles above that. My builder is a little concerned about how this will look as he will have to cut small pieces of tile to fill up the edge, which may stain once they start grouting. I'm keeping my fingers crossed and hoping for the best...

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Hi La, it comes down to personal preference if you're going for a fresh look. I quite like a gloss backsplash. What colour are your units? I would also recommend getting a few samples to compare to your worktop, not all white tiles are true whites. You might find some look more yellowy next to your worktop. Here are a few inspiration images from Pinterest of matt & gloss.

I decided to do what your thinking about (coloured grout on floor, then white grout on walls). I think it looks OK not odd, but obviously is personal opinion. Pic attached part way through work, I didn't use a grey marble but a gold vein marble. I think I would have preferred tiles lined up between floor and wall still but you don't notice too much after a bit. Gives you an idea on effect