PyGTK3, I can't Change Button and Table Backgorund Color using modify_bg method.

[changos]

#!/usr/bin/python3
import os
import time
import gi
from gi.repository import Gtk, Gdk

class GridWindow(Gtk.Window):
    def __init__(self):
        Gtk.Window.__init__(self, title="NEOTECH")
        self.grid = Gtk.Grid()
        self.add(self.grid)
        self.btnStartTest=Gtk.Button("Iniciar Prueba")
        self.btnStartTest.connect("clicked",self.StartTest)
        self.label1 = Gtk.Label("NUMERO DE SERIE")
        self.grid.add(self.btnStartTest)
        self.grid.attach(self.label1,0,1,1,1)


    def StartTest(self,widget):
        color = Gdk.color_parse('green')
        rgba = Gdk.RGBA.from_color(color)
        self.label1.override_background_color(0,rgba)
   

win = GridWindow()
win.set_position(Gtk.WindowPosition.CENTER)
win.set_default_size(150,60)
win.set_type_hint(Gdk.WindowTypeHint.MENU)
win.connect("delete-event", Gtk.main_quit)
win.show_all()
Gtk.main()