Night Shift is definitely one of the more appealing features to be added into iOS 9.3. Certain switched on users have already been experiencing this level of functionality on iOS by using the very popular f.lux app that originally made a name for itself in the jailbreak world. Apple has never officially allowed f.lux to be offered to the mainstream consumer via the App Store, as it alters how the iOS system performs, but has seemingly deemed the functionality good enough to go through the process of implementing it as an official feature of iOS for all the 64-bit devices. from an article I read just now. Pretty interesting that Apple are doing this and everyone's OK with it being compatible with what their public image they've created is: we take care of our old users better than the competition.