The grey you are seeing with her stool indicate a problem with absorption in the digestive process. I would put her back on IAMs or another high quality food to start with. I would also get a product called Prozyme. This puts necessar enzymes into the cat's system that they may be lacking during digestion. If you put her on the Prozyme and change her food, and the stool appears not to have changed in a week, you are going to have to take her into the vet as this could also be signs of liver problems. I'm attaching a link for you where you can get the Prozyme online or many pet supply stores carry it also.
Please let me know if I can help further.