title: Change color of missing values in Seaborn heatmap
body: <p>Consider the example of missing values in the <a href="https://seaborn.pydata.org/generated/seaborn.heatmap.html" rel="noreferrer">Seaborn documentation</a>:</p>
  
  <pre><code>corr = np.corrcoef(np.random.randn(10, 200))
  mask = np.zeros_like(corr)
  mask[np.triu_indices_from(mask)] = True
  sns.heatmap(corr, mask=mask, vmax=.3, square=True)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/KG0sm.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KG0sm.png" alt="Heatmap"></a></p>
  
  <p>How do I change the color of the missing values to, for example, black? The color of the missing values should be specified independent of the color scheme of the heatmap, it may not be present in the color scheme.</p>
  
  <p>I tried adding <code>facecolor = 'black'</code> but that didn't work. The color can be affected by e.g. <code>sns.axes_style("white")</code> but it isn't clear to me how that can be used to set an arbitrary color.</p>