SetBackgroundColor in android renderer causes my other form elements background color to turn black

I am implementing a custom control with renderer based on a view. I add a button to the view and handler the click event. In the click event, I want to set the background color. But when I do it seems to cause ALL the other controls to get their background color set to black. I am not sure why this is happening, and it seems like a bug to me. Setting the text color, or other elements of the control don't seem to cause any problems. Can someone explain what is happening?

I am using v2.0.1.6495 of Xamarin.Forms


[assembly: ExportRenderer(typeof(App.Controls.ImageButton), typeof(App.Droid.Renderers.ImageButtonRenderer))]
namespace App.Droid.Renderers
{

public  class ImageButtonRenderer : ViewRenderer
{
    Android.Widget.Button btn;

    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.View> e)
    {
        base.OnElementChanged(e);


        try
        {
            if (Control == null)
            {
                btn = new Android.Widget.Button(Context);
                SetNativeControl(btn);
            }
            if (e.OldElement != null)
            {
                btn.Click -= OnBtnClick;
            }
            if (e.NewElement != null)
            {
                btn.click += onbtnclick;
            }
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(@"          ERROR: ", ex.Message);
        }
    }

    void OnBtnClick(object sender, EventArgs e)
    {
        if (btn != null)
        {
            btn.SetBackgroundColor(Android.Graphics.Color.Blue);
        }
    }
}

}

and the XAML

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:converters="clr-namespace:App.Converters;assembly=App"
             xmlns:ctrls="clr-namespace:App.Controls;assembly=App"
             x:Class="App.Views.MainPage">
      <ContentPage.Resources>
        <ResourceDictionary>
            <converters:ImageMapConverter x:Key="ImgConv"></converters:ImageMapConverter>
        </ResourceDictionary>
    </ContentPage.Resources>
  <Grid BackgroundColor="White" Padding="10">
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="10*"/>
      <ColumnDefinition Width="80*"/>
      <ColumnDefinition Width="10*"/>
    </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="15*"/>
            <RowDefinition Height="65*"/>
            <RowDefinition Height="5*"/>
            <RowDefinition Height="5*"/>
        </Grid.RowDefinitions>
        <Image Grid.Column="1" Grid.Row="0" Aspect="AspectFit"  HorizontalOptions="Fill" VerticalOptions="Fill" Source="{Binding ImageMapper, Converter={StaticResource ImgConv}, ConverterParameter='App.Images.logo.png'}" />
        <Grid Grid.Column="0" Grid.Row="3" Grid.ColumnSpan="3">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="5*"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="5*"/>
            </Grid.ColumnDefinitions>
            <ctrls:ImageButton Grid.Column="0"  />
            <Image Grid.Column="2" Aspect="AspectFit" HorizontalOptions="Fill" VerticalOptions="Fill" Source="{Binding ImageMapper, Converter={StaticResource ImgConv}, ConverterParameter='App.Images.cog.png'}" />
        </Grid>
  </Grid>