Have you ever tried to use your phone in the dark with a white/light background? It can be positively glaring which is why there are some reading apps that have a night mode. Basically this makes the theme darker so that there is less glare coming off of it in low light. That being said it looks like that feature will be applied to Android M’s settings.
According to the folks at Droid-Life who took the Android M developer preview for a spin, they discovered that there are options for changing your setting’s theme. Users will need to enable developer options first but once they do, users can choose between a Light, Dark, or automatic theme, which you can see in the screenshots above.
The first two theme options are pretty obvious as to what they do, but the last one is particularly intriguing. Presumably automatic means that your phone will be able to tell whether you’re in a brightly-lit place or a dimly-lit one, and from there will be able to adjust your settings accordingly, kind of like with screen brightness with it will adjust automatically.
However according to Droid-Life, the automatic setting didn’t work the way they intended. Either this has not yet been enabled by Google or the feature is still buggy or maybe it is meant to be used differently, but either way these are just some of the changes that Google will be introducing in Android M.