About a month ago, a local contractor installed ceramic tile in our kitchen and main dining room. Upon completion the contractor informed us to let the grout cure for a month before applying sealent. So we did. Last weekend we begin cleaning the tile and grout, preparing to seal it, when we noticed that in some locations the "Malt" coloring grout had turned to a crusty green color. When you scrape through the grout, it is apparent that the green color passes all the way through to the concrete under layment. The only thing that I've noticed is green beneath the tile is the glue that was used itself. Any suggestions?? Would mositure excess moisture in the house have caused this? Should the tile have been sealed much sooner then we were instructed to do?? Please advise???