Aero is a feature of Windows which was introduced in Vista and carried over to Windows 7 as well. Although Microsoft provides some default colors for aero, you cannot actually customize the color. AeroRainbow is a freeware utility for Windows 7 which changes color of Aero windows in random order. It designed for Windows 7 and adds more fun to your desktop. The app will automatically change the aero color after the designated time (in sec).
The app does not have any interface, when you install, it provides three shortcuts on the desktop which can be used to open and close the app. If you want to change the time, you need to use the settings shortcut.
The slider sets the time after which the color is automatically changed and there is no option to choose the color.
Related Reading: Change Windows 7 Aero Color based on Weather- AeroWeather