In order to give a little personality to its iOS, the Apple company decided to change the way the status bar is displayed on iDevices. Specifically, the company set some standard "themes" that change depending on the application you have open, and in the image above you can see them all. iOS applications use the second and third, third-party applications use all of them, but to be honest, only the second seems to me to have been made by someone with a sense of design, and the rest seem to have been thrown in there for to give the feeling of change.
