I used MSI Calacatta Cressa Honed Marble Mosaic white, light grey tile for backsplash. Used VersaBond white blanco thin-set mortar. After thin-set tiles did turn yellowish-green-grey, but turned white again after 2 days. Looked perfect on the wall. I did not seal the tile. Used CUSTOM ready to use grout in platinum. Cleaned the grout right away (waited 1-2 minutes), used 2 bucket method of water for cleaning, and wiped off with microfiber towel. however tiles have tuned dark grey, not whiteish any more. Left side of pictures below is not grouted yet. its been 3 days with fan on, did got a bit better but still not white. what did I do wrong? i still have 2 walls to grout. any ideas?