White Marble Floor With Grey Grout . I just had some beautiful white calacatta marble mosaic installed in my bathroom and picked a light gray grout. I prefer dark grout in all tile flooring and the guest bath and boys bath. 3x3 carrara hex tile with delorean gray grout (simple grout from HD from www.pinterest.com The light gray is also a fine choice, but keep in mind that it will darken and maybe not match the tile color quite as well over time. The thinset and grout have absolutely nothing to do with each other. I’ve been told that i.