title: Change specific RGB color pixels to another color, in image file
body: <p>I would like to change a single color with Python. </p>
  
  <p>If a fast solution with PIL exists, I would prefer this solution.</p>
  
  <p>At the moment, I use </p>
  
  <pre><code>convert -background black -opaque '#939393' MyImage.png MyImage.png
  </code></pre>