FreeAmp Themes (.fat) files are the design and appearance of FreeAmp, including the interface color, fonts, buttons, layout, menus, and size.
FreeAmp comes with standard Themes, which you can choose from in the Preferences Themes window.
If you are the creative type, you can create a custom Theme for FreeAmp and even share it with other FreeAmp users. For a list of available Themes and detailed information on creating a custom FreeAmp Theme, point your Browser to:
http://www.freeamp.org/themes-idx.html
Note: The FreeAmp documentation is written for the default FreeAmp Theme. If you change Themes or add a custom Theme, the FreeAmp documentation will not reflect the modified Theme.