title: How to setup blending for additive color overlays?
body: <p>Is it possible in opengl to setup blending to achieve additive color overlays?</p>
  
  <p>Red + green = yellow, cyan + magenta = white, etc.. (see <a href="http://en.wikipedia.org/wiki/File:AdditiveColor.svg" rel="noreferrer">diagram</a>)</p>