One of the joys of Android is being able to use different keyboards, but even the standard keyboard has a few tricks up its sleeve. Google Operating System explains how to alter your keyboard theme.
It's a simple trick that works on any Android 4.0 or up device, though you'll need a launcher such as Nova Launcher or Apex Launcher to make the change. You can switch to keyboards from various releases dating back to Gingerbread. Hit the post for complete instructions.
Google Keyboard Themes [Google Operating System]