title: AS3 BitmapData fillRect with Transparency not working as expected
body: <p>I'm trying to use some fillRects on a 32bit BitmapData (i.e. transparency = true and bg color set to FFFF00FF (opaque magenta). For instance I use:</p>
  
  <pre><code>fillRect(rect, 0xFF0000FF);
  </code></pre>
  
  <p>This will draw an opaque blue rect, as expected, but ...</p>
  
  <pre><code>fillRect(rect, 0x550000FF);
  </code></pre>
  
  <p>This should draw a semi-transparent blue rect, right? But instead I'm getting a dark-blue rect as if the blue is mixed with black (but the background is magenta, remember, so I'd expect the blue gets mixed with the underlying magenta?).</p>
  
  <p>If I set the color value to 0x000000FF it should give me the underlying Magenta at 100% but instead I get 100% Black.</p>
  
  <p>The BitmapData is created with a 32bit ARGB so I'm  wondering what is wrong here?</p>
  
  <p>Seems this is default AS3 behavior? After creating a small test class it indeed behaves like I explained ...</p>
  
  <pre><code>package 
  {
      import flash.display.Bitmap;
      import flash.display.BitmapData;
      import flash.display.Sprite;
      import flash.geom.Rectangle;
  
  
      public class Main extends Sprite
      {
          public function Main()
          {
              stage.color = 0x000000;
              var bd:BitmapData = new BitmapData(400, 300, true, 0xFFFF00FF);
              var b:Bitmap = new Bitmap(bd);
              addChild(b);
  
              bd.fillRect(new Rectangle(0, 0, 200, 200), 0x000000FF);
          }
      }
  }
  </code></pre>
  
  <p>You'd expect the rect drawn with fillRect would be Magenta but it obviously takes the bg color of the stage. Now my question is:</p>
  
  <p>Is there a way to get the desired effect (The fillRect alpha applies to the bg color of the bitmapdata, not the Flash stage)?</p>