Google is going to announce Android N ( Probably Android 7.0 ) this year on 18 May !
Android N will come with many new features and bug fixes over Android 6.0 Marshmallow .
Android N or Android 7.0 will be coming up with Night mode option ( Light and Dark theme ) , The above screenshots are from Nexus 5 Running Android N .
Back in 2015 Google released developer preview of Android M ( Known as Android 6.0 Marshmallow now ) , Android M Developer preview came with Night Mode feature . But Google removed that feature from Official Android 6.0 Marshmallow .
But the feature will be back with Android N . Along with Dark theme , we can expect Multi-Window , No App drawer and other interesting features . Though Android N will look almost same as Android 6.0 Marshmallow and Lollipop in Interface ,