Prevent changing theme This setting disables the theme gallery in the Personalization Control Panel. If you enable this setting, users cannot change or save a theme. Elements of a theme such as the desktop background, window color, sounds, and screen saver can still be changed (unless policies are set to turn them off). If you disable or do not configure this setting, there is no effect. Note: If you enable this setting but do not specify a theme using the 'load a specific theme' setting, the theme defaults to whatever the user previously set or the system default.

(1) GPO: User Configuration\Administrative Templates\Control Panel\Personalization!Prevent changing theme (2) REG: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer!NoThemesTab