title: How to highlight regions in a pandas plot?
body: <p>I am comparing and plotting two arrays and I'd like to plot them and also highlight in some color the areas where array <code>a</code> is less than array <code>b</code>. This is the code that I am trying to work with, where <code>c</code> is places where <code>a</code> is less than <code>b</code>:</p>
  
  <pre><code>import pandas
  import numpy
  
  numpy.random.seed(10)
  
  df = pandas.DataFrame(numpy.random.randn(10, 2), columns=['a', 'b'])
  
  df['c'] = df['a'] &lt; df['b']
  </code></pre>
  
  <p>and the resultant DataFrame is:</p>
  
  <pre><code>          a         b      c
  0  1.331587  0.715279  False
  1 -1.545400 -0.008384   True
  2  0.621336 -0.720086  False
  3  0.265512  0.108549  False
  4  0.004291 -0.174600  False
  5  0.433026  1.203037   True
  6 -0.965066  1.028274   True
  7  0.228630  0.445138   True
  8 -1.136602  0.135137   True
  9  1.484537 -1.079805  False
  </code></pre>
  
  <p>Here is the beautiful example I made in ol' trusty MS Paint (RIP) that shows what I'd like to make:</p>
  
  <p><a href="https://i.stack.imgur.com/4k8Q9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4k8Q9.png" alt="enter image description here"></a></p>