Nor unusual for marble. Was it sealed before grouting? Most marble mosaics should be sealed before grouting and then again after grouting. Hopefully it just absorbed a lot of moisture and will dry and lighten up.

Where did you buy it? Chinese?

In my previous house I used a white marble water-jet cut mosaic from Artistic Tile and it did not change color when installed and grouted.

Thank you! crossing my fingers it lightens up 🤞🏻

Find a spare piece, soak it in water for a day, then let it dry out. See if there's a color change from white to gray and back again.

What color thinset did you use? That may bleed thru some as well, especially on marble.

My Italian Carrara marble tile that was installed in my bathroom turned darker after being set - it took several days for it to lighten. There are many posts on Houzz re: marble turning dark after being installed. If I wouldn't have read posts related to this issue prior to having my marble tile installed, I would have freaked out! However, I did quite a bit of research prior to purchasing marble for my shower walls.

As long as a white thinset (mortar) was used, it should lighten up after a bit. It may not lighten up to the color it was prior to setting - but it should be close.

Do you know the country of origin for your marble? You should find out from the retailer.

The thinset was light gray

" The tile was white when we put it up, then used optic white grout and now the tile is completely gray. "

" The thinset was light gray "

Now we may be getting somewhere. Marble is very adsorbent. You never answered (that I saw anyway), was the marble tile sealed BEFORE install?

Honestly im not sure. it was put on the gray thinset and after a day it was still white. It didn’t turn gray until after grouting. 🤔

Just one day. it was grouted yesterday

How long did the install wait before grouting and I think the wall thta is partially done looks white to me so not sure what you are showing

Give it a week to dry out.

The wall that is partially done is white. the tile didn’t turn gray until after applying the white grout

A fair amount of water gets put on the tile when they are cleaning the grout, which is why they should have been sealed before, and a bonus step is to apply grout release over the tiles, to make cleaning the grout easier/quicker so less water is used.

I put a test pc of the tile in a bowl of water for 12 hrs and it didnt change color. The tile changed color right after grouting. Within minutes. The grout was optic white. Make this make sense 🤪😬