title: SolidColorBrush with Opacity on a Black background
body: <p>I am doing the following to fill a rectangle with a certain opacity.</p>
  
  <pre><code> SolidColorBrush fillColor = new SolidColorBrush(myColor);
   fillColor.Opacity = 0.3;
   rectangle1.Fill = fillColor;
  </code></pre>
  
  <p>The rectangle is part of a user control that is on a Black background. The problem is that I am getting the opacity on a White background. How to change it as if opacity is applied on the color on a Black background. </p>
  
  <p>The following is the color I get for a green color fill.
  <img src="https://i.stack.imgur.com/qXGcq.png" alt="enter image description here"> (i.e as overlaid on white background) What I need is something like this. <img src="https://i.stack.imgur.com/uiMDU.png" alt="enter image description here">  (i.e as overlaid on black background)</p>