What causes grey stool?

Sorry this is gross but I need help! Haha anyways, so today i went to the bathroom and my stool was grey.. It's definitely not normal for me. Ive had some problems with eating for the past year where I get diarrhea after I eat (frequently) but never grey stool. I went to get a ultrasound to see if my gallbladder was okay but that came up fine. And next week another test for my gallbladder.. Could grey stool be related? Help! Thankss:)