I think leaving the wall white around the marble slab is nice - but if you are wanting to incorporate color, then I would suggest picking the lightest color in the marble and painting the surrounding area in that. You could also do wood paneling in a light color and have the profile of the paneling come out, so that it box frames the marble.

Choose a medium tone found in the marble and paint all the walls! As it stands now, there is no drama and the marble makes no statement.

Agree with leaving the wall as is to highlight the slab.

Thanks for the feedback. As @mermaide said in the message, I feel there is no drama right now, that is why I was wondering if adding some color to the wall would make the slab pop. But the slab has blacks and white and very mild brown and as a result I am having a hard time picking a color. I even thought about black just for that wall...

So are all the walls going to be the cream color that is currently around the slab? Because, unless it's the light being tricky, the slab wall looks like it's cream but the wall next to it looks more of a true white.

Is the floor a brown adobe color? Does the marble wall have any brown or beige?
I like a medium grey on the walls, but the floor color throws me

Don't know what the floor is or what the vanity will be. You cannot get more dramatic than that wall, so without knowing what the other finishes are and with the wood windows I'd wait till it's more finished. That wall really stands alone but you must make the woods work so since it has some brown in it I think you're fine for now.

This reminds of this photo. They have a different stone around the feature slab.
https://www.houzz.com/photos/34-whiskey-ridge-contemporary-bathroom-denver-phvw-vp~2534065

Thanks @lucampers, I fell in love with the slab the moment I saw it :) @printesa, once I saw the slab the picture on Houzz you shared was the inspiration!

@lefty57 that is exactly why I was thinking of black.
@mermaide the floor is currently covered in paper to prevent it from getting too dirty while work is happening near & on it such as the tub. I have attached a picture of floor before it was grouted.
@Craig, attaching some pictures for you - floor before it was grouted (it is currently covered with paper), the vanity counter is a ceaser stone called London fog and the cabinet is a rich espresso brown.

Looks great!!
-Angeline, GKB

I would try (you can always change it!) a greige colour to warm the room - I think the walls are very stark.

On all walls

@cpsin I really like the idea of greige.
Attaching pictures of were we are now.

I would do all the walls a dove gray.

If you paint around the slab, consider not taking the paint all the way to the edges of the walls, but using paint color, perhaps a very subtle color, as a kind of "mat" or frame around the slab. I think carrying the paint to the edges could look awkward.

A thin outline of blue stone. About 1 inch wide.