Timber tones, but take a photo of your samples and put it up in comments. Also a picture of your kitchen.

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.

I currently have the same problem It quite braves to use White on the floor ( I know you said grey) but we are toying with as it works well with the grey bath we have chosen Have a think about swapping it around to have black on the floor which works great with a contrasting colour bath (white) Also think about contrasting colour for taps (black taps against white or grey tiles)

Option 3 has a terrazzo-look tile which references the previous and original bathroom. The concrete look tiles will date, and look quite daggy in ten years time. Best of luck, Dr Retro of Dr Retro House Calls