Is there a way to change the display from an iOS app to filter out the blue light?
There is a f.lux app, but it is only available through cydia, so I figured iOS might not give regular apps the power to do this?
If you mean globally, then no. That's the reason F.lux is only available through Cydia as you mentioned.
If you mean only for your own app then you could simply tint all graphical elements in a more yellow tint though some clever tricks.