I would love to have f.lux on my un-jailbroken iPhone. Currently I use Twilight App on a Nexus by my nightstand during the night because of how harsh the iPhone screen is in the dark (even with brightness turned down all the way).
There's a similar, more flexible, open source app you can sideload via Xcode here: https://github.com/anthonya1999/GoodNight . I use it on my non-jailbroken iPhone and iPad. Does the trick for me (all orange, all the time).
