Index: wp-content/themes/twentytwelve/js/theme-customizer.js
===================================================================
--- wp-content/themes/twentytwelve/js/theme-customizer.js	(revision 22124)
+++ wp-content/themes/twentytwelve/js/theme-customizer.js	(working copy)
@@ -21,7 +21,7 @@
 	// Hook into background color change and adjust body class value as needed.
 	wp.customize( 'background_color', function( value ) {
 		value.bind( function( to ) {
-			if ( '#ffffff' == to || '#fff' == to || '' == to )
+			if ( '#ffffff' == to || '#fff' == to )
 				$( 'body' ).addClass( 'custom-background-white' );
 			else if ( '' == to )
 				$( 'body' ).addClass( 'custom-background-empty' );