title: matplotlib modified color map with white as zero
body: <p>Some of the standard <code>matplotlib</code> <code>cmap</code>s, such as <code>viridis</code> or <code>jet</code> show dark colors in <strong>small values</strong>. While this is what I need, I like them to show nothing, i.e. white background if the value is <strong>exactly zero</strong>. For non zero values the usual colors of that color map are fine.</p>
  
  <p>Is it possible to do this?</p>