fixes Issue matplotlib#1693

Explicitly trim rgbFace to length 3 so that the string formats do
not blow up.

lib/matplotlib/backends/backend_ps.py

@@ -587,7 +587,7 @@ def draw_markers(self, gc, marker_path, marker_trans, path, trans, rgbFace=None)
             if rgbFace[0]==rgbFace[1] and rgbFace[0]==rgbFace[2]:
                 ps_color = '%1.3f setgray' % rgbFace[0]
             else:
-                ps_color = '%1.3f %1.3f %1.3f setrgbcolor' % rgbFace
+                ps_color = '%1.3f %1.3f %1.3f setrgbcolor' % rgbFace[:3]
 
         # construct the generic marker command:
         ps_cmd = ['/o {', 'gsave', 'newpath', 'translate'] # dont want the translate to be global