Pretty much any time you turn a monitor while it's on you'll get that. The earth's magnetic field affects color CRT's. It happens to television sets and computer monitors too.
All color monitors/TV's have built in degaussing circuits that fire when the set is turned on from being cold. So, shut the game off, put it where you want it, wait a half hour to an hour, and turn it on.
This is a common problem in cocktail games. People turn the game on with the monitor flipped up, do some adjustments, flip the monitor down, and now it's all out of whack. Gotta let it sit off for a while so the built-in degauss circuit will fire again.
Modern computer monitors usually have a manual degauss circuit you can activate from a front panel control. Try this for some fun - rotate your computer monitor 90 degrees, turning it onto it's side. The colors will get all screwed up as the earth's magnetic field affects the CRT. Use the front panel degauss control to fix it. Then, put the monitor back sitting up, and the colors are once again out of whack. For bonus points, do this to a co-worker's computer when he's out of the room.
-Ian