title: Make pie chart with percentage readable in grayscale
body: <p>I have a source code to generate pie chart</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from matplotlib.pyplot import savefig
  import numpy as np
  import matplotlib.gridspec as gridspec
  
  plt.clf()
  plt.cla()
  plt.close()
  labels_b = ["Negative",  "Positive"]
  dev_sentences_b = [428, 444]
  test_sentences_b = [912, 909]
  train_sentences_b = [3310, 3610]
  
  gs = gridspec.GridSpec(2, 2)
  ax1= plt.subplot(gs[0, 0])
  ax1.pie(train_sentences_b,  autopct='%1.1f%%',
          shadow=True, startangle=90)
  ax1.axis('equal')
  ax1.set_title("Train")
  
  ax2= plt.subplot(gs[0, 1])
  ax2.pie(dev_sentences_b, autopct='%1.1f%%',
          shadow=True, startangle=90)
  ax2.axis('equal')
  ax2.set_title("Dev")
  
  ax3 = plt.subplot(gs[1, 1])
  ax3.pie(test_sentences_b, autopct='%1.1f%%',
          shadow=True, startangle=90)
  ax3.axis('equal')
  ax3.set_title("Test")
  
  ax3.legend(labels=labels_b, bbox_to_anchor=(-1,1), loc="upper left")
  
  plt.savefig('sstbinary', format='pdf')
  </code></pre>
  
  <p>Result <br>
  Color picture <br>
  <a href="https://i.stack.imgur.com/juelZ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/juelZ.jpg" alt="color-pie-chart"></a>
  <br>
  and grayscale <br>
  <a href="https://i.stack.imgur.com/BWpxt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BWpxt.png" alt="grayscale"></a></p>
  
  <p>The grayscale version is a bit difficult to read. Is there any suggestion to make grayscale pie chart readable in black-and-white printing ?</p>