Gtk Background transparent

[Paolo <prallo gmail com>]

Hi! I'm developing an gnome applet with python. It's an easy and stupid
applet, but I'd like to make it more nice. My applet is a eventbox  with
inside a label. All works fine but the background is gray. The gnome panel
is transparent and the applet should be the same if we want a good look &
feel.
How can I make the applet transparent?
The piece of code is the following:
....
eb = gtk.EventBox()
label = gtk.Label('text')
eb.add(label)

# I think the backgound of the EventBox (eb) should be edited

widget.add(eb)
...