This is a simple tweak in which your keyboard color and background keeps changing constantly according to the apps you are using currently. This tweak colorize your keyboard base on the dominant color of the apps icon that you are in.
Loing for a way to customize that boring stock keyboard color within your iOS, ColorYourBoard can change the colors for you. Its an application that solely helps you to change the color of the keyboard to anything you like. The app includes features like color wheel , something you can find in image editing applications, select your brightness and transparency colors as well.