There is a white film of dust on the slate& grout

We recently remodeled 50% of our house from re-texturing walls to new dark multi color slate flooring in all the trafficked areas. Even though our slate floor was sealed before the texturing and painting was done, there is still a white film of dust on the slate and grout. I had the slate professionally cleaned and the white film still remains. How can I get the natural dark color back?  Thank you so much. Sandra.