Xamarin.Forms NavigationPage BackgroundImage - Android

Hi there!
I am trying to setup an image as a background for a NavigationPage on a Xamarin.Forms project.
Here is how my App.cs file looks like:

public class App
    {
        public static Page GetMainPage ()
        {   
            var navigation = new NavigationPage(new StartPage());
            navigation.BackgroundImage = "navbg.png";
            return navigation;
        }
    }

On the Android project I have the image in the following path:

/Resources/drawable/navbg.png

However, the image never shows up as a background for the NavigationPage no matter what I try.

Any help will be much appreciated!

Thanks!