private static void OnIsPrimaryChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
        {
            ColorPoint target   = obj as ColorPoint;
            bool       oldValue = (bool)args.OldValue;
            bool       newValue = (bool)args.NewValue;

            if (oldValue != newValue)
            {
                target.OnIsPrimaryChanged(oldValue, newValue);
            }
        }