LATICRETE®-SPECTRALOCK® 1 Pre-Mixed Grout 

It looks great but give it some traffic. I contacted Latecrete and they never responded after noticing darker gray was turning brown from lite foot traffic from dirty shoes. Scrubbed and still has brown in it. For such resistant advertised grout, they won't tell you how to clean. Does take sealer so something doesn't add up, because it absorbs dirt. Been told by tile distributers to scrap down the top layer and reapply - what? You know how much work that is on 400'sf?