Problem with gtk_tree_selection_select_path: background color does not change

[Carlos Pereira <jose carlos pereira ist utl pt>]

Hi list,
I need to select multiple rows in a treeview,
directly from my code, in MULTIPLE selection mode.
This is a very simple treemodel, only one column
with a string.

Unfortunately, although gtk_tree_selection_select_path()
seems to select the indicated rows, the background color
of the rows do not change.

For example, running this code:
path = gtk_tree_path_new_from_string ("1");
gtk_tree_selection_select_path (selection, path);
path = gtk_tree_path_new_from_string ("3");
gtk_tree_selection_select_path (selection, path);

and then:
gtk_tree_selection_selected_foreach (selection,
static_foreach_list, data);

shows that the second (1) and fourt (3) rows have indeed
been selected, but the background color remains unchanged...

So my question is: how can I force GTK to change the 
background color of the selected rows?

Many thanks for your help, I searched the archives for
this mailling list, I did see this question posted, but
not a working answer... the same for the web...

Carlos