title: Filling the area between plots after setting X axis limits
body: <p>I'm having difficulty to set X axis specific limits when I plot two curves on the same graph.</p>
  
  <p>My data has two curves (PERMEABILITY and POROSITY) and DEPTH will work like an index. So I managed to plot them on the same graph and to fill the areas between them with some help. Here is my code:</p>
  
  <pre><code>df = pd.DataFrame({'DEPTH': [100, 150, 200, 250, 300, 350, 400, 450, 500, 550],
         'PERMEABILITY': [1000, 800, 900, 600, 200, 250, 400, 300, 100, 200],
         'POROSITY': [0.30, 0.25, 0.15, 0.19, 0.15, 0.10, 0.15, 0.19, 0.10, 0.15]})
  
  f, ax1 = plt.subplots()
  
  ax1.set_xlabel('PERMEABILITY') 
  ax1.set_ylabel('DEPTH')
  ax1.set_ylim(df['DEPTH'].max(), df['DEPTH'].min())
  
  ax1.plot(df['PERMEABILITY'], df['DEPTH'], color='red')
  ax1.tick_params(axis='x', labelcolor='red')
  
  ax2 = ax1.twiny()
  
  ax2.set_xlabel('POROSITY')
  ax2.plot(df['POROSITY'], df['DEPTH'], color='blue')
  ax2.tick_params(axis='x', labelcolor='blue')
  
  # convert POROSITY axis to PERMEABILITY
  # value-min / range -&gt; normalized POROSITY (normp)
  # normp*newrange + newmin -&gt; stretched POROSITY to PERMEABILITY
  z=df['POROSITY']
  x=df['PERMEABILITY']
  nz=((z-np.min(z))/(np.max(z)-np.min(z)))*(np.max(x)-np.min(x))+np.min(x)
  
  # fill between in green where PERMEABILITY is larger
  ax1.fill_betweenx(df['DEPTH'],x,nz,where=x&gt;=nz,interpolate=True,color='g')
  # fill between in yellow where POROSITY is larger
  ax1.fill_betweenx(df['DEPTH'],x,nz,where=x&lt;=nz,interpolate=True,color='y')
  plt.show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/vInU8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vInU8.png" alt="enter image description here"></a></p>
  
  <p>But when I try to set specific limits for X axis, this filled area does not follow the new 'curve size' as you see on the left image below. My result should be like the image on the right (I did this one on Paint). For example, if I add:</p>
  
  <pre><code>ax1.set_xlim(0, 1500)
  ax2.set_xlim(-0.10, 0.45)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/HDXSy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HDXSy.png" alt="enter image description here"></a></p>
  
  <p>Someone could help me with this? Thanks in advance!</p>