Getting python Tkinter to recognize display

I am trying to get the python GUI package Tkinter running on the BeagleBone Black (debian Jessie) to connect to the display. I get this error when I run a simple Tkinter test program:

root@beaglebone:/boot# python /home/debian/oqy/
No protocol specified
No protocol specified
Traceback (most recent call last):
  File "/home/debian/oqy/", line 3, in <module>
    root = Tk()
  File "/usr/lib/python2.7/lib-tk/", line 1813, in __init__ = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: couldn't connect to display ":0.0"

What more do I have to configure?