How do I turn off the contrast

Do you mean System Preferences - Accessibility (Universal Access on 10.6 & prior) - Display - Enhance Contrast ?

If so, drag the slider back to Normal, then look at Keyboard Preferences - Keyboard Shortcuts to disable the key combinations which may have altered it.

If not that - please explain in more detail.

Open the System Preferences and click on the Universal Access icon. You may have accidentally invoked "Enhance Contrast". If so, move the slider all the way to the left to disable it.