Change some widget font and fore ground ok,some fail,why?

[sandy_21 <sandy_21 sina com>]

Hello:
    I use Gtk+2.0.0, redhat 7.2
    as the gtk reference said,  to change widget font and color
use gtk_widget_modify_fg(),gtk_widget_modify_font()
    I make some experiment on some widget ,the conclusion is
simple widget such as GtkLabel,GtkEntry the above two api work
correctly,but complecate widget like GtkButton,GtkTreeView,GtkTextView
so on,it doesn't work,the foreground color is always black,and the font 
is default
    So,I wonder is it because Gtk2.0 bug or it must be implemented in 
other way?
Any hint? Thanks a lot