title: Black and white colorbar
body: <p>I usually use the "seismic" colorbar of matplotlib.</p>
  
  <p>For a publication need, I have to use black and white colors. I would like to keep the same aspect as "seismic" (i.e., blackest values for highest min and max values), as shown on the picture:</p>
  
  <p><a href="https://i.stack.imgur.com/rZ5Py.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rZ5Py.png" alt="enter image description here"></a></p>
  
  <p>How do I make this conversion?</p>