title: Legend not showing up in Matplotlib stacked area plot
body: <p>I am creating a stacked line/area plot using <a href="http://matplotlib.org/api/axes_api.html#matplotlib.axes.Axes.fill_between" rel="noreferrer">plt.fill_between()</a> method of the pyplot, and after trying so many things I am still not able to figure why it is not displaying any legend or labels (even when I provide them in the code). Here is the code:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy
  
  a1_label = 'record a1'
  a2_label = 'record a2'
  
  a1 = numpy.linspace(0,100,40)
  a2 = numpy.linspace(30,100,40)
  
  x = numpy.arange(0, len(a1), 1)
  
  plt.fill_between(x, 0, a1, facecolor='green')
  plt.fill_between(x, a1, a2, facecolor='red')
  plt.title('some title')
  plt.grid('on')
  plt.legend([a1_label, a2_label])
  plt.show()
  </code></pre>
  
  <p>Here is the image generated (note that the legend shows empty box instead of labels):
  <img src="https://i.stack.imgur.com/d9aim.png" alt="empty legend box at the top">    </p>
  
  <p>Help!</p>