I had a real shocking surprise when I went to my tub surround tile job today. The grout that we applied the day before had dried two different colors – one was the desired light brown (Polyblend “Haystack”), and the other was white! The discoloring occured randomly, sometimes a small spot about the size of a pea, sometimes for a few lineal feet, and sometimes over a few square feet. We cleaned between the tiles thoroughly before grouting, mixed the grout well, and the bag from the store seemed untampered with. I do tile installations quite a bit and have never seen this kind of ghosting before. Any ideas what may have happened?