error tk

Error tk
===================================================
from tkinter import *

v0 = Tk()
v0.mainloop()
v0.config(bg="black")
=============================================
C:\>a.py
Traceback (most recent call last):
  File "C:\a.py", line 5, in <module>
    v0.config(bg="black")
  File "C:\Python34\lib\tkinter\__init__.py", line 1270, in configure
    return self._configure('configure', cnf, kw)
  File "C:\Python34\lib\tkinter\__init__.py", line 1261, in _configure
    self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
_tkinter.TclError: invalid command name "."

C:\>