Handling themes simply and effectively

Hi
For my app i need to have two themes, normal and dark (how original..!)
But i don't really know how to handle that with Xamarin.

In my settings i have a switch allowing the user to choose between the two themes. It saves the value as a bool into a settings plugin.

So far i just succeded to change the background according to that bool, this way. And i'm sure it's not proper way at all.

 protected override void OnAppearing()
        {
            var image = "";
            if (AppSettings.GetValueOrDefault("switch_night", false))
            {
                image = "fond_fonce.png";
            }
            else
            {
                image = "fond_clair.png";
            }
            BackgroundImage = image;

            base.OnAppearing();
        }

But i need to change not only the background, all this elements have to change:

• colorPrimary in styles.xml android project
• colors of all buttons (defined in xaml now)
• Colors of some ios elements (haven't spend much time on this platform yet)

I read about custom renderers, but haven't really understood deeply how it work. Is it the best solution, or there is easier way to achieve?

Thanks