Please tell me you guys aren't serious....
Demo mode is when the unit changes through all of the backgrounds/ screen savers etc. etc. etc. indefinitely.
The screen flashing to a negative image is called the screen-saver mode, or something like that, it alternates between a positive and negative image when you are using the basic text-display mode, to preserve the pixels from being burned out while displaying non-moving text at high contrast for long periods of time. It's completely and thoroughly in the manual, as well as how to disable it.
People like you are the reason i have to read countless threads about how 'hard to use' kenwood decks are. You've got a really expensive, yet great head unit, why wouldn't you take the time to read through the manual and learn how to use it? Have someone else read it to you if you're having trouble, but for god's sake, features that you don't know how to use may as well not be there.