Hi aimeelou2002, Stunning tiles! Either grout option would work. The darker will really make the tiles the feature in the room. Personally I'd probably go the softer grey however, the tiles will still pop as the light grey will still contrast against the brilliant white, but not be so dramatic as the charcoal which will appear black against the White (especially if everything else is white /muted). Good luck with your decision, and I'm sure it will be beautiful whatever you choose!

Ouch! redoing the job means scraping out the old grout and replacing. In my limited experience tilers hate doing this and may miss bits, I don't think the grout is as solid afterward either, ok on walls not so good on busy floors. If the grout hasn't been sealed and given that it is so absorbent anyway it should be simple to recolour, just test first as it may change colour when it dries. Then use a quality tile and grout sealer, worth the time imho. I would hesitate to tell a professional tiler which brand of grout to use unless you have experience, they differ in quality, colour is up to you of course.

I agree on the soft grey for the floor tiles. I think anything else would detract from the pattern of the lovely floor tiles. I can see why you asked for help with the wall grout. I can think of 4 different reasons why I'd choose different colours! Maybe look at some similar tiles (real life or photos) with similar coloured tiles and different grout colours.

We are renovating three bathrooms, all with dark grey 600 x 600 floor tiles, white 300 x 600 wall tiles laid vertically, and a feature wall with textured subway tiles laid vertically. In the ensuite, the feature tiles are white (blanc), in the main bathroom they are palest pink (rose), and in the powder room they are palest green (vert). https://www.equipeceramicas.com/en/portfolio-item/la-riviera/  My question is about choosing a grout colour and whether it should be the same colour for the wall tiles as for the feature wall tiles? The feature tiles are textured and have slight colour variations (ie. not all one single shade), as you can see in the link. I'm thinking of using the Ardex misty grey. Any advice would be great! Thanks.