I am assuming you are referring to the Theme "Windows Modified" that you switched off. The theme was what set your background color. If you do not want to go back to using the theme, then you can click over to the next tab (Desktop) and set whatever background color you want. This will be the background for both monitors since you are in extended mode for Hoster.
You don't mention whether you are using XP or Vista. If it is XP go to the Control Panel, Sounds and Audio Devices. Turn off the sounds (No Sounds) again. By changing the theme this was reset to defaults. I am not sure if Vista is the same for these.
Is that quick enough?
