Changing the color of the iOS keyboard might be old news on a jailbroken device. Then ColorfulKBD Pro comes along. With this jailbreak tweak installed, iOS 7 users are treated to a new color combination every time the keyboard is opened.
ColorfulKBD Pro can also add a custom background image directly from the Photos app to the keyboard. The colors that are randomly displayed can be constrained to a specific range with sliders in Settings -> ColorfulKBD Pro.
The minimum and maximum hue, as well as minimum and maximum brightness can be selected. Other options include a slider for color saturation and a kill switch to toggle the tweak off entirely. ColorfulKBD Pro keeps the look of the iOS 7 keyboard fresh every time.
ColorfulKBD Pro is available from the BigBoss repo on Cydia for $0.99. Jailbreak iOS 7.1.x with Pangu to start customizing iOS. Check here for instructions on how to jailbreak iOS 7.0.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.