title: How to show legend in missingno matrix?
body: <p>So far, I have managed to spawn a legend box and have managed to put it outside the chart. But it is showing the same colours for both the labels (white and white) whereas I would prefer it to show white and gray.</p>
  <pre><code>import missingno as msno
  
  msno.matrix(X_train, figsize=(15,10), sparkline=False, p=0);
  plt.legend(['missing','not missing'],loc='center left', bbox_to_anchor=(1, 0.5))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/6NVNB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6NVNB.png" alt="" /></a></p>