def change():
if var.get() == 0:
label['bg'] = 'red'
elif var.get() == 1:
label['bg'] = 'green'
elif var.get() == 2:
label['bg'] = 'yellow'
window = Tk()
window.title('Світлофор')
window.geometry('400x400')
var = IntVar()
var.set(0)
red = Radiobutton(text =' Червоний', variable=var, value=0)
green = Radiobutton(text = 'Зелений', variable=var, value=1)
yellow = Radiobutton(text = 'Жовтий', variable=var, value=2)
button = Button(text = 'Змінити', command=change)
label = Label(width=20, height=10)
red.pack ()
green.pack ()
yellow.pack ()
button.pack ()
label.pack ()
window.mainloop ()