VoltKey keyboard started with a simple design. It has a flat UI with changeable background colors. All of the keys disburse into a grid view, so the keys harder to reach is larger than others. VoltKey can also recognize gestures, to enhance your experience. Gestures such as, swipe left to delete the last word. You can also swipe up from certain keys to insert a number instead of a letter. iPhone 6 and and iPhone Plus versions have one hand mode. This mode will allow you to type with one hand.
Here are the instructions to change the background color of the keyboard extension.
1) Launch the keyboard extension
2) Swipe up from (▼ or ▲) button
3) A menu will prompt you to change the keyboard background color.