OverElement.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:local="clr-namespace:GridSample" 
             x:Class="GridSample.GridSamplePage">
    
    <Grid VerticalOptions="CenterAndExpand">
      <Grid.RowDefinitions>
         <RowDefinition Height="200" />
       </Grid.RowDefinitions>
        
      <Grid.ColumnDefinitions>
        <ColumnDefinition Width="10*" />
      </Grid.ColumnDefinitions>

     <Image Grid.Row="0" Grid.Column="0" Source="mountainPhoto" HorizontalOptions="FillAndExpand" Aspect="AspectFill"/>
     <Label Grid.Row="0" Grid.Column="0" Text="Mountain Green" TextColor="White" VerticalOptions="End" HorizontalOptions="FillAndExpand">
          <Label.BackgroundColor>
              <Color x:FactoryMethod="FromHsla">
                  <x:Arguments>
                    <x:Double>0</x:Double>
                    <x:Double>0</x:Double>
                    <x:Double>0</x:Double>
                    <x:Double>0.6</x:Double>
                  </x:Arguments>
                </Color>
           </Label.BackgroundColor>
     </Label>
    </Grid>
</ContentPage>