title: Change Colours of all Black Pixels in Pygame
body: <p>I'm making a program with the Pygame that changes the overall colours of inserted pictures.  It works fine, but  now I'd like to change specific portions of the picture - only black.  Is there a method that changes the colours of <em>all</em> black pixels to an alternative colour?</p>
  
  <p>I've already tried using <code>surface.set_at()</code>, <code>surface.get_at()</code> as well as a few others.  Help please? :)</p>