Yep. Seen this before.
What you got is an application-boosted problem. This usually comes from using a program (especially games) where the screen is brightened (or darkened, or whatever) when you're using it. Some programs that do this are UnrealEd, Half-Life, UT2k3, some versions of AutoCAD and 3DSM, and especially MOH.
If when using the program you somehow cause it to crash or close prematurely, you can run into this error. Even a reboot will sometimes not fix the "stuck" view alterations. One way to fix this is to run that application again (if it's a game, actually run and play the game) and then carefully close the program down through its menus (not by a console command or the X-kill). Often, a hard-boot will fix this problem too.
Mid case scenario: you reinstall your drivers for yer vid card.
Your problem is a little different, what with the video setting, but I suspect this is no different. It is likely you set the high-contrast, ran some game that made it "stuck" and now can't change it back.
Worst case scenario: Contact your g-card manufacturer about the issue and see what they say (check their site too).
