title: Matplot drawing rainbow lines to X-axis without request
body: <p>Matplotlib has started drawing rainbow lines to the X-axis without request. Sometimes it still draws the normal plot, but often not.                 </p>
  
  <pre><code>import numpy
  import matplotlib
  G=numpy.zeros(100)
  for i in range(50):
      G[i+50]=50-i
      matplotlib.pyplot.plot(G)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/zju8I.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zju8I.png" alt="enter image description here"></a></p>
  
  <p>What is causing this behavior and how do I turn it off permanently? I have the latest version  of matplotlib installed, running python 3.6, anaconda distribution <code>4.5.5</code>.</p>