Customize: Fix clearing of a color control's setting by using proper empty value.

Props stevehenty.
Fixes #30280.



git-svn-id: https://develop.svn.wordpress.org/trunk@33938 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/customize-controls.js

@@ -1655,7 +1655,7 @@
 					control.setting.set( picker.wpColorPicker('color') );
 				},
 				clear: function() {
-					control.setting.set( false );
+					control.setting.set( '' );
 				}
 			});