BlackBerry Theme Builder overview
Themes determine the look and feel of BlackBerry® devices. A theme can change the appearance and structure of the Home screen, the application list, the banner, dialog boxes, title bars, and other elements of the user interface such as fonts and background colors.
Users can choose from themes that are preloaded on their BlackBerry devices, or they can download a theme in a .cod file format.
You can build your own theme using the BlackBerry® Theme Builder. The theme layout is a template for the Home screen and the application list. Users can access all applications from the application list. At a minimum, include the date, time, battery power level indicator, and wireless coverage indicator in the Home screen banner. The BlackBerry Theme Builder includes the following layouts:
Catalogs can help you organize the project resources such as images and colors that you can access at any time.
When you open the BlackBerry Theme Builder, the Quickstart screen opens. You can click a recent theme that you worked on to open it, you can open an existing theme, or you can create a new theme. The Quickstart screen lists resources to help you develop your theme if you need more information.

The BlackBerry Theme Builder workspace includes a preview area for viewing how your theme appears on the selected BlackBerry device, buttons for designing each of the customizable elements (such as the Home screen, banners, and other elements of the UI on the BlackBerry device), and tools for arranging and resizing elements on the BlackBerry device screen.

You can download and install the BlackBerry® Smartphone Simulator to test new themes on your desktop, before you distribute them to BlackBerry devices or you can install the themes directly on a BlackBerry device.