I have a question regarding the default alpha value for an Artist.
Why is it 1.0 instead of None? The color conversion code takes into
account if alpha is None and having it default to something other than None
makes it impossible for any Patch to have a fill_color specified as an RGBA
value (and possibly other Artist sub-classes). Should this be something
else, or should the Patch.set_facecolor method pre-process the incoming color
value and set any specified alpha as appropriate (I hope not since this would
cause the color value to be processed several times)?