Google Keyboard 5.1-which can technically be installed on versions of Android as old as Jelly Bean-contains a couple exclusive new feature for those on the latest Android N preview. Most notably, you can now pick from a variety of themes, including different color schemes for the keyboard, or selecting a custom background image. 5.1 also comes with a new set of emoji from the Unicode 9 update. Unfortunately, neither of these features work on older devices yet, but it's a nice glimpse into what's coming for everyone else.
Google Keyboard 5.1 | APK Mirror via Android Police