title: How to fill rainbow color under a curve in Python matplotlib
body: <p>I want to fill rainbow color under a curve. Actually the function matplotlib.pyplot.fill_between can fill area under a curve with a single color. </p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  x = np.linspace(0, 100, 50) 
  y = -(x-50)**2 + 2500
  plt.plot(x,y)
  plt.fill_between(x,y, color='green')
  plt.show()
  </code></pre>
  
  <p>Is there a knob I can tweak the color to be rainbow? Thanks. </p>