title: Change DWORD color alpha channel value
body: <p>I have a starting color: 0xffff00ff, which is a:255, r:255, g:0, b:255.</p>
  
  <p>The goal is to change the alpha channel of the color to be less opaque based on a percentage. i.e. 50% opacity for that color is roughly 0x80ff00ff. </p>
  
  <p>How I've tried to reach the solution:</p>
  
  <pre><code>DWORD cx = 0xffff00ff;
  DWORD cn = .5;
  
  DWORD nc = cx*cn;
  </code></pre>