title: Plotting graph with ax.axvspan
body: <p>I'm trying to make a plot with axvspan, but it doesn't get anything plot and doesn't give me an error. Any idea? here the image and the code.<a href="https://i.stack.imgur.com/yroG3.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yroG3.jpg" alt="enter image description here" /></a></p>
  <pre><code>fig = plt.figure(figsize=(15, 6))
  ax = fig.add_subplot(111)
  
  
  xtime       = np.linspace(1,372,372)
  #sp3 = sp3.reshape((360))
  
  ax.plot(xtime, sp12, 'black', alpha=1.00, linewidth=2)
  ax.fill_between(xtime, 0., sp12, sp12&gt; 0., color='blue', alpha=.75)
  ax.fill_between(xtime, 0., sp12, sp12&lt; 0., color='red',  alpha=.75)
  
  
  plt.xlabel('Years')
  plt.ylabel('SPI')
  plt.title('SPI-12 Macuelizo[ (1985-2015)', fontsize=12)
  ax.axhline(-0.6, color='red', label='SPI - 0.6')
  ax.axhline(-1.3, color='magenta', label='SPI - 1.3')
  ax.axvspan(1997, 1998, color='magenta', alpha=0.7)
  
  ax.set_xlim(0, 372)
  ax.set_ylim(-4, 3)
  ax.set_xticklabels(range(1985,2016,1*4))
  
  
  plt.grid(True)
  plt.legend()
  ax.autoscale_view()
  
  plt.savefig('SP12_macuelizo.jpg')
  </code></pre>