My stools are brown and gray. what could cause that?

Change in bowels: The amount, color, frequency of stool varies with foods, speed of emptying of the GI tract, medications ; supplements ingested, gut flora (unique for each individual), additives (like blood), subtractions (like absent bile), infection, inflammation, ; other factors. If stool pattern has changed, is unusual for you, ; the change persists, or is accompanied by other symptoms, see your doctor.