title: how to access custom prop_cycle colors?
body: <p>I've defined a custom color cycler in a text file, and am invoking it via <code>plt.style.context()</code>.  The cycle I've defined has 12 colors.  When annotating the plot, if I try to access my custom cycler colors using color strings, <code>'C0'</code> through <code>'C9'</code> work but <code>'C10'</code> throws <code>ValueError: Invalid RGBA argument: 'C10'</code>.  All 12 values are definitely in there. Contents of style file <code>style.yaml</code>:</p>
  
  <pre><code>axes.prop_cycle : cycler('color', ['332288', 'CC6677', 'DDCC77', '117733', '88CCEE', 'AA4499', '44AA99', '999933', '882255', '661100', '6699CC', 'AA4466'])
  </code></pre>
  
  <p>Test script:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  data = np.c_[np.zeros(13), np.arange(13)].T
  labels = list('abcdefghijklm')
  
  with plt.style.context('style.yaml'):
      # just to prove that the colors are loading correctly:
      cycle = plt.rcParams['axes.prop_cycle'].by_key()['color']
      print('{} colors: {}'.format(len(cycle), cycle))
      # now the actual plotting:
      fig, ax = plt.subplots()
      ax.plot(data)
      for ix in range(data.shape[1]):
          ax.text(x=1, y=data[1, ix], s=labels[ix], color='C{}'.format(ix))
  </code></pre>
  
  <p>The result (notwithstanding the <code>ValueError</code> that stops it plotting after 10 labels) is that the lines follow my custom cycler colors, but the text labels use the matplotlib default cycler colors (see screenshot).  How can I get the text to appear using the custom cycler colors defined in the external YAML file?</p>
  
  <p><a href="https://i.stack.imgur.com/F2E7v.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/F2E7v.png" alt="screenshot of example plot"></a></p>