title: Xamarin Forms transparent element with border
body: <p>I am using a <code>Frame</code> to create a border on various elements (Grid, StackLayout &amp; ContentView) and need to now make the elements transparent; I tried setting the opacity of the Grid etc. but of course the <code>Frame</code> colour impacts the actual background colour.</p>
  
  <pre><code>&lt;ContentPage BackgroundImage="some_image.png"&gt;
    &lt;!-- ... --&gt;
    &lt;Frame BackgroundColor="Gray" Opacity="0.7" Padding="1" Margin="10"&gt;
      &lt;Grid BackgroundColor="White" Opacity="0.7" Margin="20"&gt;
        &lt;Label Text="..."/&gt;
      &lt;/Grid&gt;
    &lt;/Frame&gt;
    &lt;!-- ... --&gt;
  &lt;/ContentPage&gt;
  </code></pre>
  
  <p>The <code>Grid</code> is rendered as expected but now the Frame grey background makes the white grid appear grey. Ideally I would like a white transparent Grid with a solid grey border, is this possible in Xamarin?</p>
  
  <p>(Im using shared Xamarin forms project targeting iOS &amp; Android)</p>