title: XAML Performance: Set alpha channel of a brush vs. Opacity of FrameworkElement
body: <p>For a given XAML layout that requires a semi-transparent white (to provide a glass-like effect in this case), which method would be preferable to set the transparency and why?:</p>
  
  <ol>
  <li>Set the alpha channel of the brush. E.g. <code>#12FFFFFF</code></li>
  <li>Set the opacity of the FrameworkElement itself, leaving the brush as 100% white.</li>
  </ol>
  
  <p>Also, is the answer different between WPF (4.0) and Silverlight?</p>