How do you override the opacity of a parent control in WPF?

I was able to achieve something like this in pure xaml using a Brush to paint the main grids background.
This way only parent grid will have its opacity set and its child elements won’t inherit it.

<Grid x:Name="LayoutRoot">       
      <Grid>
        <Grid.Background>
            <SolidColorBrush Color="Black" Opacity="0.5"/>
        </Grid.Background>
        <Grid.RowDefinitions>
          <RowDefinition Height="0.333*"/>
          <RowDefinition Height="0.333*"/>
          <RowDefinition Height="0.333*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
          <ColumnDefinition Width="0.333*"/>
          <ColumnDefinition Width="0.333*"/>
          <ColumnDefinition Width="0.333*"/>
        </Grid.ColumnDefinitions>

        <Grid Grid.Column="1" Grid.Row="1" Background="Red" />
      </Grid>   
</Grid>