I'm guessing that he means the Cabbie default theme, which is black and yellow. But a clarification would be useful.
In any event, vanman, the manual should explain how to reset your settings using a key combination at startup (I don't remember offhand how to do it on the Gigabeat and don't have access to the manual at the moment). Alternately, you can connect your Gigabeat via USB and delete the config.cfg file to reset your settings to default.