Using GTK's to build transparent backgrounds

["Raul Z.T." <plaf citt cl>]

Hi everyone , 
              Well after hours searching in the documentation of GTK+ 
without luck , i finnaly decided to ask the experts . Actually im building 
an application that displays text using Pango , i modified the background 
collor of the drawing area without problem , but how i can give it some 
transparency/opacity to that area? i  need it as transparent as possible , 
my idea is to get the same effect that gives transparent rxvt's and others 
, how i can do that? 

I am using perl-gtk2 (1.21)
  Glib 1.120 
  GTK+ -> 2.8.15-1

on fedora core 5

Many thanks in advance!
Raul