title: How can I set different opacity of edgecolor and facecolor of a patch in Matplotlib
body: <p>I am trying to plot a set of triangles with different orientations and sizes. The inner overlapped shape is what i wanted, which is the darkest area. 
  But when I set opacity (alpha) in mpatches.RegularPolygon, the edges become transparent too. 
  How can I solve this problem?
  Thank you!</p>