title: how to generate the shaded regions with matplotlib
body: <p>I was trying to get the figure 5 in this <a href="http://pubs.rsc.org/en/content/articlepdf/2016/sc/c5sc02678d" rel="nofollow noreferrer">paper</a> but I couldn't generate two shaded regions that indicate the errors of 1 and 2 kcal/mol. Each shaded region must be in a different color as in paper. How can I do that?</p>
  <p><strong>My code:</strong></p>
  <pre><code>#!/usr/bin/python
  import numpy as np
  import pylab as plot
  import matplotlib.pyplot as plt
  import numpy, scipy, pylab, random
  from matplotlib.ticker import MultipleLocator
  import matplotlib as mpl
  from matplotlib.ticker import MaxNLocator
  
  color = &quot;#252525&quot;
  gray = &quot;#777777&quot;
  
  with open(&quot;input.txt&quot;, &quot;r&quot;) as f:
      x=[]
      y=[]
      z=[]
      
      for line in f:
          if not line.strip() or line.startswith('@') or line.startswith('#'): continue
          row = line.split()
          x.append(float(row[0]))
          y.append(float(row[1]))
          z.append(float(row[2]))
      
  
  fig = plt.figure(figsize=(3.2,2.2), dpi=300)
  ax = plt.subplot(111)
  
      
  plt.xlim(-2, -12)
  plt.ylim(-2, -12)
  ax.xaxis.set_major_locator(MaxNLocator(6))
  ax.yaxis.set_major_locator(MaxNLocator(6))
  
  ax.xaxis.set_minor_locator(MultipleLocator(1))
  ax.yaxis.set_minor_locator(MultipleLocator(1))
  
  plt.plot(x,y,'o',color=&quot;black&quot;, ms=3, mec=&quot;black&quot;)
  plt.plot(x,z, color='gray' , linestyle = &quot;dashed&quot;, dashes=(2,2))
          
  plt.xlabel('Experimental (kcal/mol)', fontsize=8)
  plt.ylabel('Predicted (kcal/mol)', fontsize=8)
  
  for axis in ['top','bottom','left','right']:
    ax.spines[axis].set_linewidth(0.5)
  
  plt.subplots_adjust(top=0.95)
  plt.subplots_adjust(bottom=0.18)
  plt.subplots_adjust(left=0.14)
  plt.subplots_adjust(right=0.95)
  
  
  plt.tick_params(axis='both', which='major', labelsize=7)
  plt.tick_params(axis='both', which='minor', labelsize=0)
      
  plt.savefig(&quot;output.png&quot;, dpi=300)
  </code></pre>
  <p><strong>Input file:</strong></p>
  <pre><code>-2      -2.0    -2
  -3      -3.5    -3
  -4      -5.0    -4
  -5      -7.0    -5
  -6      -6.0    -6
  -8      -10.1   -8
  -10     -10.0   -10
  -12     -12.0   -12
  </code></pre>
  <p><strong>Obtained output:</strong></p>
  <p><a href="https://i.stack.imgur.com/Z16x9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Z16x9.png" alt="enter image description here" /></a></p>