title: Set a colormap under a graph
body: <p>I know this is well documented, but I'm struggling to implement this in my code.</p>
  
  <p>I would like to shade the area under my graph with a colormap. Is it possible to have a colour, i.e. red from any points over 30, and a gradient up until that point?</p>
  
  <p>I am using the method fill_between, but I'm happy to change this if there is a better way to do it.</p>
  
  <pre><code>def plot(sd_values):
  
      plt.figure()
      sd_values=np.array(sd_values)
      x=np.arange(len(sd_values))
      plt.plot(x,sd_values, linewidth=1)
      plt.fill_between(x,sd_values, cmap=plt.cm.jet)
      plt.show()
  </code></pre>
  
  <p>This is the result at the moment. I have tried <code>axvspan</code>, but this doesnt have <code>cmap</code> as an option.  Why does the below graph not show a colormap?</p>
  
  <p><img src="https://i.stack.imgur.com/QTcsq.png" alt="enter image description here"></p>