transparent markerfacecolor

Hi, I'm using matplotlib v0.82 an I would like know if there

    > is the possibility to set the markerfacecolor to
    > "transparent", so that I can see two markers when they are
    > one above the other.

With plot, which generates lines, in principle you should be able to
set the alpha channel. This controls the transparency of the edge and
the face (they aren't currently separable). However, in testing, I
just noticed that the transparency is not respected for markers with
the *Agg backends, which I think is a consequence of the way I
optimized marker drawing several releases back. I'll have to
investigate further. Also, transparency is not respected across
backends, eg PS, GTK, WX.

You can use transparent markers with scatter:

    from pylab import *
    x,y = rand(2,100)
    scatter(x, y, s=300, alpha=0.5)

It would be useful to have a markerfacecolor='None' option, which
worked across backends, even those which don't support transparency.
If you think this is sufficiently useful, please file a sourceforge
support request.