title: How to create matplotlib colormap that treats one value specially?
body: <p>How can I create a matplotlib colormap that maps <code>0</code> (and <em>only</em> <code>0</code>) to white, and any other value <code>0 &lt; v &lt;= 1</code> to a smooth gradient such as <code>rainbow</code>?</p>
  
  <p>It seems neither <code>LinearSegmentedColormap</code> nor <code>ListedColormap</code> can do this.</p>