Your dashboard has a House Lights toggle in the top bar, the small switch next to your avatar. Flip it once and the dashboard chrome, panels, and forms shift from the default dark canvas to a warm cream. Flip it back any time.
This is a personal-comfort setting. It does not change how your public fan page looks. Your fans always see the color theme you picked under Profile → Appearance → Public Page Theme. House Lights only changes what you see, on your dashboard and on BCKSTG pages like Help and Playback in the same browser.
The choice saves automatically. Next time you sign in from the same browser, you land back in whichever mode you last used.