clé recommends the use of unpigmented grout. When we use the term 'unpigmented' grout we are indicating that you don't want any added dyes. You'll want to look for unsanded cement based grout in either natural gray or a color matching the lightest shade in your pattern (if applicable). Natural gray is typically pigmented with actual portland cement (hence the 'natural' part).
The right grout is key but what's even more important is getting the grout off the face of the tile immediately. It should be applied in smaller sections (2'x2' or 3'x3') to help facilitate quick clean up. Please keep in mind that even with grout release, if the grout is allowed to set up on the the face of the tile it could cause grout haze and staining due to tiles porous nature. If you have further questions please don't hesitate to reach out - we can be reached at firstname.lastname@example.org and (415) 887-9011.