why modify_style(GtkRcStyle style); has no effect?

["Yannick Barbeaux" <ybarbeaux gmail com>]

Hello,
I am trying to modify the colors of individual widgets in my apps,
as i can see there are 3 different ways to do it:

1-   SET_STYLE : works fine

ex:
  r_gtkStyle = r_entry->get_style();
  r_gtkStyle->set_text(Gtk::STATE_NORMAL, myGdkColor);
  r_entry->set_style(r_gtkStyle);

2-  DIRECTLY MODIFY ON WIDGET : works fine

ex:
   r_entry->modify_text(Gtk::STATE_NORMAL, myGdkColor);

3-  MODIFY_STYLE : does nothing at all

ex:
   r_gtkRcStyle = r_entry->get_modifier_style();
   r_gtkRcStyle->set_text(Gtk::STATE_NORMAL, myGdkColor);
   r_entry->modify_style(r_gtkRcStyle);


can anyone tell me why the modify_style has no effect at all in my code?