title: Multiple Transparency Layers
body: <p>Please be kind, I'm new to this....</p>
  
  <p>I have an application that I'm developing where I need to take a PNG image, which has a transparency layer, and treat another color (I'm thinking of using RGB( 1, 1, 1 ), since it's so close to pure black that I can hard-code it) as a separate transparency layer.  The reason for this is that I have a background image sitting behind the PNG image that I would like to still display as my sprite gets filled (by adding a progress bar to the sprite), and I only want the portions of the sprite that aren't of the given color to reflect the color fill of the progress bar.  In this way, I can avoid having to deal  with vector computations for the outline of the image within the sprite, flood the area outside of the discernable image with my new "transparent" color, and be on my merry way.</p>
  
  <p>I've tried using shaders, but they seem to be less than helpful.</p>