avoid background painting GtkWindow

[Georg Mitterböck <mitterboeck lunatone com>]

Fred Morcos asked some time ago:

I'm just trying to tell GtkViewport not draw the default background
with gtk_widget_set_app_paintable() function, and setting background
pixmap gdk_window_set_back_pixmap (vp->window, NULL, FALSE);

it still draws the gray background.
does anybody have a clue on how to do it?
thanks in advance

I have the same problem. Can anyone please tell me how to disable background painting of my 
GtkWidget *window;
window = gtk_window_new( GTK_WINDOW_TOPLEVEL);

thanks in advance.

Georg