Interesting you should ask. I am dealing with a similar problem. My reearch suggest that the mix you suggest is the "old timers" way of enhancing the color of porous tiles and stone. Check out the following modern products; Tile Labs "Stone Enhancer and Sealer"' available from Custom Building Products or Enrich N' Seal from Aqua Mix Inc. These are penetrating sealers that bring out the color and seal the surface. You may have to strip and remove previous treatments. Experiment on an inconspicuous area. I found that these are not commonly stocked products in Home Depot or ***** (although they carry the Tile Lab and Aqua-Mix line). I ended up ordering it on line from fct@florencecarpetandtile.com in South Carolina.