A MahApps theme is two choices: a base theme, which decides whether the application is light or dark, and a colour scheme, which decides the accent. Two base themes times twenty-three schemes gives forty-six resource dictionaries, and picking one is a single line in App.xaml.

ThemeManager is the class behind everything a theme does after startup: switching, detecting, following the Windows setting, and building themes that are not in the box. It lives in ControlzEx, not in MahApps.Metro, so every snippet here starts with