title: pyplot.plot() modifying line color cycle
body: <p>I want to plot some data obtained through measurements each with their fit.
  I will plot 6 measurements on each figure, but I want each measurement data plot have the same color as its fit. From one measurement data plot to the next I want the defalut color cycle of matplotlib.</p>
  
  <p>First, the data if loaded as following:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import matplotlib as mpl
  import numpy as np
  data1 = np.genfromtxt('data1.txt')
  fit1 = np.genfromtxt('fit1.txt')
  ...
  </code></pre>
  
  <p>Then the problem, I can of course redefine the colour sequence in rcParams, like the following:</p>
  
  <pre><code>ColourSeq = []
  ColourSeqOriginal = mpl.rcParams['axes.color_cycle']
  for ind in range(len(ColourSeqOriginal)):
      ColourSeq.append(ColourSeqOriginal[ind])
      ColourSeq.append(ColourSeqOriginal[ind])
  mpl.rcParams['axes.color_cycle'] = ColourSeq
  </code></pre>
  
  <p>but this seems complicated.</p>
  
  <p>The simplest thing seems to be:</p>
  
  <pre><code>plt.figure()
  plt.plot(xdata, data1, xdata, fit1, '???')
  plt.plot(xdata, data2, xdata, fit2, '???')
  plt.plot(xdata, data3, xdata, fit3, '???')
  </code></pre>
  
  <p>'???' being the command option which I don't don't know if some exists that will prevent plt.plot incrementing the color value for the given data.
  But from one plt.plot() invocation to the next, I need to have the normal color increment.</p>