title: Plotting with a transparent marker but non-transparent edge
body: <p>I'm trying to make a plot in matplotlib with transparent markers which have a fixed color edge . However, I can't seem to achieve a marker with transparent fill. </p>
  
  <p>I have a minimum working example here:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  x = np.arange(10)
  y1 = 2*x + 1
  y2 = 3*x - 5
  
  plt.plot(x,y1, 'o-', lw=6, ms=14)
  plt.plot(x,y2, 'o', ms=14, markerfacecolor=None, alpha=0.5, markeredgecolor='red', markeredgewidth=5)
  
  plt.show()
  </code></pre>
  
  <p>I tried two techniques I found online to achieve this:
  1) Setting alpha parameter. However, this makes the marker edge transparent too, which is not the desired effect.
  2) Setting markerfacecolor=None, although this has no effect on my plot</p>
  
  <p>Is there a solution to this please?</p>