I'd love to see more images of some of the tiles you produce.

The patterned ones come in a mixed box, as in a mixture of all patterns. You could have all patterns or throw in the plain one with slight marble effect (Hex Carrara Bianco) as in the attached photo from a Beaumont tile brochure. If your room is small you could consider the lighter version which is white and grey - Hex Blend Bianco.

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.

Ania, can you post photos when it is finished. It will be good to see those colours combined. I also love that inspiration photo and have it saved. I don't know what particular thing makes that bathroom stand out but it is beautiful. I want those exact same colours in my bathroom but a too scared to use timber tiles as I am scared they will date so am bringing in timber via accessories such as picture frames (I think). What is the grey tile in your photo and where is it from...it is very nice.