import gtk

def style_set_cb(label, style, textview):
    textview.modify_base(gtk.STATE_NORMAL, label.style.bg[gtk.STATE_NORMAL])

hbox = gtk.HBox()
label = gtk.Label("Hello")
textview = gtk.TextView()
textview.props.buffer.props.text = "World"
label.connect("style-set", style_set_cb, textview)

hbox.add(label)
hbox.add(textview)

w = gtk.Window()
w.add(hbox)

w.show_all()

gtk.main()