I always have the problem with mushrooms. Its color turns to gray in just a few days. I find an interesting method for preserving mushroom on the internet. First, I wash mushrooms, then I cut them in the quarter. Secondly, I blanch them in boiling water for two minutes. After that, I refresh mushrooms in cold water ad let them cool down and drain. Finally, I placed them and put them in the freezer now finally I enjoy white good looking mushrooms in my recipe. I used these sites: http://www.mushroomthejournal.com/preserving-mushrooms/, http://www.sceltamushrooms.com/preserving-mushrooms, and http://www.wikihow.com/Preserve-Fresh-Mushrooms.