All Files Changing the Theme Colours The Harmony interface is set to a dark theme by default. You have the option of switching to a light theme. How to change the interface theme From the top menu, select Edit > Preferences (Windows/Linux) or Harmony Essentials > Preferences (macOS) . The Preferences dialog box opens. Select the General tab. In the Options section, deselect the Use Dark StyleSheet option to use the light theme. Restart Harmony.