Latisse has never been shown to change the color of the iris. The product began as an eye drop for glaucoma, and it was only in this use that eye color change occurred. Since it was repackaged into the topical eyelash form of Latisse, no patients have reported this event. Since Allergan has a patent on the active ingredient, you are unlikely to find an alternative with bimatoprost as the active ingredient. And I have seen no data that shows something else works.
The starting color of the eye is also an issue. Hazel and light brown eyes were the ones that darkened with the glaucoma prep. The incidence of that was very rare. Blue eyes do not darken.