About 4 weeks ago, I had limestone tile installed as a fireplace surround and I was told that the darker areas would lighten as the tile dried. No noticeable change has taken place in the 4 weeks which leads me to believe either the tiles are still holding moisture or whatever product was used to adhere them to the wall, discolored them during the process. Thoughts? (top photo taken about 4 weeks ago. Bottom taken today) Thank you.