ProgressBar and transparency

["zze-DEPREZ Olivier FTRD/DMI/SOP" <olivier deprez rd francetelecom com>]

Hello, 

I'm using progressbars, and I'd like to "separate" a single progressbar
into different parts, one in red, one in blue for exemple ...
As I didn't find any way to do this, I tried to juxtapose two
progressbars, one on the other. My problem so far now is to make the
background of the first one transparent, so the second one could be seen
...
I have read some topics on making a widget transparent/translucent,
talking about gtk_widget_shape_combine_mask(), but I can't see any
precise help on it ...

Regards, 

Olivier