So far I have not seen any color change in the culator bag. It is supposed to turn colors for different metals, and comes with a chart to match the color to the metal. I did not have any stains in the pool, because I just finished removing them and balancing all my chemicals at the beginning of this swim season. I put the bag in to see if it does change color if I do start to precipitate metals, or if the pool stains. If I get any stains, then the culator does not work.