Google is rolling out the v5.1 of the Google Keyboard app for Android. This was part of Android Nougat beta but is now available to older versions of Android as well.
The main change here is expanded theme options. While previously you had black and white, you now get multiple color options. Most importantly, you can also set a custom background image for the keyboard and adjust the opacity till it’s just right for you.
The keyboard also technically supports the Unicode 9 emoji standard but you need OS level support to type those and that’s only available on Nougat for now.