My suggestion is first talk to the builder to see what instructions he gave the tiler as i'm sure he doesn't want a dissatisfied client. Most tilers will check with the builder before grouting especially when a colour is not specified in a contract. I would then ask if the grout could be replaced, from the looks of it it will only be a couple of hours work. There is nothing worse than having to look at something you are not happy with. I would not use the paint product as it will alway look like it is covering a mistake. White will look better. Make sure the mixer body is waterproofed or you will have a leak in your wall, the membrane should lap onto the body from the wall if it is done well. All the best.

Thanks Nicole!! We actually went for white grout too in the end, and stacked them (mid century modern house, we thought it fitted better overall). I agreed with you that I wanted the detail of the tile to shine, not the shape of the tile. We still need to paint the rest of the room, etc., but I'm pleased. We had them sealed and used a supposedly more stain resistant grout (Davco Colour Elite). We loved the designs so much we put the 150mm blue jeans version in our pantry!! Thanks again for your reply. Enjoy your new space.

What a beautiful tile! Rule of the tump - always match the grout to the tile. Specially with such a strong patterned tile, otherwise the grout also becomes a clashing pattern. I'd pick light grey to avoid pure white cleaning issues. I have these type of tiles in my patio, you will have to be seal them with penetrating sealer after installation, but other then that you will love them forever

What grout have they used? I thought there's a newer grout doesn't need sealing, what's it called, epoxy grout? Also check what they used where the vertical meets the horizontal as it's supposed to be a flexible product but builders don't always take the time to do that correctly, by the time the tiles start cracking they'll be long gone.