No mouse or rat naturally has colored droppings. Their metabolism is very fast and so they produce quite a number of droppings everyday. As many as 150 for a healthy mouse. The rodent bait we often use to exterminate mice is usually colored green or red. This is for human safety reasons more than anything. Since the bait goes through a mouses system so fast the color is retained in the stool and thus it comes out green or red depending.