Treeviews: changing the color of column headers

["Juan L. Freniche" <fdesp87 gmail com>]

I am trying to change the color of the column headers of a treeview, 
with no sucess at all.

I tried:
    for each column in the treeview:
        when defining the column, set_widget (col, label)
        now show the widget (i.e., the label).
    Then  show the treeview.
    And now:
        for each column in the treeview:
            get_widget (col)
            get_parent // the alignment
            get_parent // the hbox
            get_parent // the button
            modify bg (button, state normal, some gdk color) // tried 
also with modify base
Result: nothing, header columns blank

I also tried in the rc file (still using gtk 2.xx):
style "TreeHeaderStyle"
 {
  bg[NORMAL] = "blue"  # tried also with base
 }
widget_class "*.GtkTreeView.GtkButton" style : highest "TreeHeaderStyle"

Result: nothing, header columns still blank

The global gtkrc is the default one and my particular gtkrc is
# Auto-written by gtk2_prefs. Do not edit.
gtk-theme-name = "Nimbus"
style "user-font"
{
    font_name="Sans 10"
}
widget_class "*" style "user-font"

I change the theme to several others and no success.
I know that some years ago the same question was made, I followed the 
recommendations given there. No success.

I would appreciate any help. Thanks.
Ah, in Win32.