GammaThingy
Changes screen gamma on iOS, no jailbreak required
Important Information
This project is in no way associated with f.lux.
I talked with Britta Gustafson about this idea/project at jailbreakcon 2015, and she felt that I should contact the developers of f.lux before publicly releasing anything to do with changing the screen temperature. I know they don't have a monopoly on it, but they care very deeply about what they work on and have poured their lives into a piece of software which they feels improves the lives of others (which it does). Aside from that, f.lux has a home on practically every jailbroken phone, and I wouldn't want to hurt the feelings of anyone so important to the jailbreaking community by making a cheap knockoff of their work just for fun. Because of this, I purposely have not added an open source license to the project and am intentionally retaining copyright for the code, meaning that it may not be redistributed (in code or compiled form) without my permission. You may think it's dumb to have open sourced it then, but I've learned a lot from open source projects over the years and value having as much code publicly available to read as possible, even if it's under copyright. This is especially useful for things like this project, where very little other related public code exits. So basically, it's open source so people can learn from it.
Besides all that, this is not nearly as complex or well-designed as the actual f.lux application and most likely will never come close. The developers of f.lux have spent a lot of time perfecting what they do.
Compiling
This can't be compiled for or run in the simulator so don't try it, it won't work. If you get errors make sure all frameworks are linked correctly, especially IOKit and IOMobileFramebuffer.