title: Python/Matplotlib -> to_rgba: Invalid rgba arg
body: <p>I'm trying to plot contours and have previously used a RGB tuple to specify the color (only one for all contours) - however, now I get a ValueError from to_rgba:</p>
  
  <pre><code>ValueError: to_rgba: Invalid rgba arg "1"
  to_rgb: Invalid rgb arg "1"
  cannot convert argument to rgb sequence
  </code></pre>
  
  <p>Here is an example:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  grid = np.random.random((10,10))
  contours = np.linspace(0, 1, 10)
  </code></pre>
  
  <p>Now this works!</p>
  
  <pre><code>plt.contour(grid, levels = contours, colors = 'r')
  plt.show()
  </code></pre>
  
  <p>But this does NOT work!</p>
  
  <pre><code>plt.contour(grid, levels = contours, colors = (1,0,0))
  plt.show()
  </code></pre>
  
  <p>Am I doing something wrong or is this bug (/new feature) in Matplotlib? Thanks.</p>