m3459 I don't even need a shower curtain but your choice is so very fabulous I'd love to know it's origin. I have a friend who is redoing a bathroom and I am helping him make design decisions. I'd love to suggest that curtain. And @Lydia (KAZZA design) I love the wall hung floating cabinet you've chosen to show the O.P. Can you also give out the secret of where to find it or one very much like it. Is it wood? It looks Italian with about a gazillion coats of lacquer. Thank you both for adding your design ideas (and I'm just a "lurker").

Definitely use the white grout for the white subway tiles...... I would use a light grey grout for the entire floor including the inset and the grey tiles. The grey grout should be as light or lighter then the carrara marble...........

If you want to try to work with it, then I would suggest again that you move to a grout that has yellow/gold undertones to try to tie the tile into the countertop better. Below is a travertine backsplash grouted in TEC cornsilk. It helps to bring out the creams/yellows in the stone. The color chart that you have is from Custom Building Products. Below is a photo with Alabaster on the far right. The middle is Ivory from TEC and the left is Cornsilk from TEC. The Alabaster has gray undertones. The Ivory and the Cornsilk have yellow undertones. Test an enhancer/sealer on spare tile and see which tones it brings out. If it brings out yellow/golds then use it. If it brings out beige or brown, then use a sealer that is not an enhancer. Before you decide on any grout, test some samples and make sure. Once it's on, if you don't like it then tearing it all out is about your only option.

gray. you don't want white on a shower floor. any light or medium gray will look fine. try Mapei FlexColor CQ. it's an acrylic stain proof grout. avail at Lowes. Also, make sure you seal the tops (just the top) of those pebbles before you lay them or grout them. use a good impregnating sealer (don't let it drip down the sides).