Boundary Color

I was wondering how or if you could change the color of the boundary from black to white or w/e color you wanted. I believe I played a map that was supposed to be an island floating in the sky and they had white w/e around the land. I assume it was boundary. Just a random question I had been wondering for awhile. If you know anything on the subject please explain it to me.

er actually the boundary is supposed to be a shadow i think >_>. if you looked around in Advanced -> Gameplay Interface u could probably change it