What do iodine solution and vitamin C have anything to do with each to do with each other? its for my project?

plz help! this is for my science fair project and i rlly rlly need to knw because the project says that when vitamin C is added into the iodine solution mixed with distilled water and cornstarch, it is supposed to turn lighter in color (which was indigo/blue) can someone plz tell me why is that?