According to Chainfire, the night mode and color adjustment features from Chainfire3D and the original CF.lumen Gingerbread apps are frequently requested. So frequent, in fact, that they're back for KitKat+ devices as CF.lumen on the Play Store.
If you've ever used f.lux for your PC, you know basically what to expect here - color temperature adjustments based on the time of day, bringing tones more in line with your eyes' expectations when the sun goes down. CF.lumen can also match artificial light sources, and has a sleep mode which turns your screen red, so as to not disturb your "night vision." Users can also override the service any time, or have CF.lumen use the device's light sensor to make adjustments.
Besides all that, CF.lumen offers additional filters including inverted colors, manual adjustments, and colorblind optimizations.
Of course there are other options for some of this functionality (like Twilight), but none seems quite as complete as Chainfire's solution.
If you've been hoping Chainfire would bring this functionality into the current era, or if you're a rooted user who wants awesome automatic color temperature adjustments to ease your strained eyes (or to experience Android's UI in monochrome), hit the widget below.
Source: Chainfire (Google+)