When you installed LS Cerbie, you had the option to prevent themes from changing your system colours. If you failed to use this option, just open up personal.rc and follow the instructions in the 'personal settings: syscolor' section.

If the wallpaper changing is being done by the theme through LSThemeInstaller, just run LSThemeInstaller, click the 'Settings' button, and choose not to apply wallpaper. (Note: after 'OK'ing the settings, you can click 'Cancel' to get out of the theme installer without installing a theme, your changes will still be saved.)

There are LiteStep modules that change the wallpaper too though - you'll have to read their documentation, or just comment them out to disable them.