I've tried so many different "screen filter" apps that kind of work but not really well. This is a different approach which stays crystal clear and still allows complete color changes. The functionality is very similar to Cyanogenmod's RenderFX feature that was a real boon to people reading in bed etc. Unfortunately that hasn't been around since CM7 or CM6.
Anyways this new app is by Chainfire and it's called CF.Lumen. Here's a playstore link: https://play.google.com/store/apps/d...hainfire.lumen
Note that it requires root.
If you use a screen filter app then you owe it to yourself to try this. The difference is *very* noticeable.
Feel free to post any alternatives you know of because as far as I know there isn't a single one that isn't an overlay filter which basically sucks.