Thank you for your post.
Marble subway tile with grey grout.
Still a very pretty look which we love.
For anyone checking back on this i am having a new house built and had a carrara marble 3x6 subway tile backsplash put in the kitchen with absolute black granite.
As a backsplash installer that s all i do i must agree with you that pale grey is indeed the most popular grout colour for standard 3 6 white subway tile.
Use a non sanded grout to protect both the marble and the grout from discoloring too much.
Now when you go with a black tile and a white grout you are going to see that visually like with white tile and black grout things start looking a bit busier and you do make out the shapes of the tiles more so than you would if it was all tonal.
Especially when looking at it in the daylight.
Five years ago mosaic on mesh was the most popular option for a backsplash accounting four about 75 of installations.
I went with tec standard white grout and it came out very yellow or antique white against the tile.
White grout is a risk in bathrooms though as everyone mentions.