iOS 9 Themes
Apple is slowly opening up support for third-party developers with the option to choose your iPhone keyboard, and with that choice users can add color to the iPhone keyboard like never before. Some of the options are amazing, while others are gaudy, but it lets users choose what they want.
Read: Best iOS 8 Themes
Instead of simply allowing users to change the iPhone background and lock screen, it would be great to see iOS 9 themes that let users change system colors slightly to match their current look, wallpapers or just their favorite colors.