Mimicing disabled fonticon behaviour with a custom icon

When a button with a FontIcon is disabled, it will be greyed out automatically. However, with a custom icon on a button, this does of course not happen. What is the best approach for mimicking this behvaiour? I understand you need two icons.

 <AppBarButton.Icon>
       <ImageIcon Source="{StaticResource CustomIcon}"/>
 </AppBarButton.Icon>

So I think the best approach to do this is to create an eventhandler for IsEanbled on the button and change the icon there.

 private void AppBarButton_IsEnabledChanged(object sender, DependencyPropertyChangedEventArgs e)
 {
     var button = sender as AppBarButton;
     var icon = new ImageIcon();

     if (button != null)
     {
         icon.Source = button.IsEnabled
             ? (SvgImageSource)App.Current.Resources["EnabledIcon"]
             : (SvgImageSource)App.Current.Resources["DisabledIcon"];

         button.Icon = icon;
     }
 }