Mac OS X displays inverted image colors (white on black, reverse type)
Your computer may display a reverse image if certain keys are pressed at the same time. Depending on your configuration, it may be black and white or inverted color, as shown below.
Mac OS X 10.0, Mac OS X 10.1, Mac OS X 10.2, Mac OS X 10.3, Mac OS X 10.4, Mac OS X 10.5
Press the Control-Option-Command-8 key combination. This is actually a feature of Universal Access that you can toggle.