Fix PatchCollection bug 2732455 by letting to_rgba handle 'none'

svn path=/branches/v0_98_5_maint/; revision=7025

Author: efiring

lib/matplotlib/colors.py

@@ -318,9 +318,17 @@ def to_rgba(self, arg, alpha=None):
         Returns an *RGBA* tuple of four floats from 0-1.
 
         For acceptable values of *arg*, see :meth:`to_rgb`.
+        In addition, if *arg* is "none" (case-insensitive),
+        then (0,0,0,0) will be returned.
         If *arg* is an *RGBA* sequence and *alpha* is not *None*,
         *alpha* will replace the original *A*.
         """
+        try:
+            if arg.lower() == 'none':
+                return (0.0, 0.0, 0.0, 0.0)
+        except AttributeError:
+            pass
+
         try:
             if not cbook.is_string_like(arg) and cbook.iterable(arg):
                 if len(arg) == 4: