If you cannot see the settings to change them, you should probably do a
System Restore. If you can see the settings it's pretty easy to change them.
You have created a "Custom" theme. There are several approaches to what you
want.
You can reset the theme to the default "AERO" setting in Control Panel,
"Personalizations", "Window Color and Appearance", "Open classic appearance
properties for more color options", "Color Scheme" drop box set to "Windows
Aero" and OK. This would reset everything.
You might continue the special setting by using the Control Panel,
"Personalizations", "Window Color and Appearance", "Open classic appearance
properties for more color options", "Color Scheme" drop box set to "Windows
Aero" , click "Advanced" button, set "Item" drop box to "3D Objects", set
color to white.
Exactly what you want for your desktop colors can all be set in the Items
drop box in various properties dialogs.