it turns slightly yellow right away, in days. properly stored, SSKI should last a decade.
now this is what i make from pure Iodide and water. other manufacturers may use additional ingredients and such that could change the appearance and the shelf life. they might be better or they might be worse, i dont know.
it takes low pH and oxygen to break apart KI into its constituants. thats why when SSKI hits an empty stomach with nothing else in the stomach to interfere, there will be some elemental released. whether it is enough to matter is another guess.