You might be pleasantly surprised how different it will look when you change the wall colour. Perhaps if you didn't that first, you'd not need to change the grout. I'd agree; if the tiles aren't symmetrical then a darker grout line would highlight this. I'd also agree that dark grey would look great - you have this in your floor mats and it looks nice against your gorgeous floor tiles. We went grey in our ensuite. Hubby was concerned it would be dark, but we love it. Worst case - if you change your mind, paint is an easy swap. Good luck ;)

Agree with the above. For your pattern / feature tile to stand out more, the other tile should be extremely simple / plain. The colour of the chevron tile isn't very clear, if it is a grey, it may be worth going for a pale grey grout (similar to mapei ultracolor moon white or silver grey), so it can be used all round with chevron as well as the plain white tiles or alternatively, going for a complete contrast and matching the grout to the tiles they're going with. Hope this helps.

I think it depends on the chosen tile. Ceramic tiles have rounded edges so grout lines look bigger anyway. With porcelain the edge is very crisp and for me 2mm looks better

Some of these trades are useless. I wanted a new internal door so chose someone recommended to me. He said he’d pop round to quote. He didn’t turn up. He called me the next day full of apologies saying he forgot. He came the next day and quoted. Six week wait to fit it, but that was fine. Fitting day came, he said he couldn’t make it. Booked another day, he cancelled. He tried to rebook and I said sorry I’m finding someone else. He cried but I’ve bought the door! Sorry mate, goodbye. I could go on about all the trades who have let me down or did a bad job despite being recommended. My sister had a terrible time with a carpenter (friend of our nephew) who trotted off to Howdens with her money to buy several doors. He never came back! It was only when her husband named and shamed him on Facebook that he posted the cash through her letterbox in the early hours. Motto: never pay up front! Your tiler has done a nice job by the look of it so try not to worry too much.