We recently ran into a problem at with a few kids at school who had ‘accidentally’ activated High Contrast Mode in Vista by accidentally pressing Shift+Alt+PrtScrn, and couldn’t turn it off again. I say ‘accidentally’ because we’ve recently seen kids doing this to each other deliberately as this month’s Favourite Game of the Month™ (previous winners of Favourite Game of the Month™ include using a hotkey to rotate the screen so it is upside down, and vandalising Wikipedia).

High Contrast Mode is an accessibility feature in Windows that causes the desktop theme to switch off of Aero (or whatever is currently set) onto an almost completely black scheme with white text. It also disables the desktop wallpaper and changes the background colours of applications like Word to black, so it appears the user is typing white text onto black paper.

Despite repeated use of the Shift+Alt+PrtScrn shortcut, High Contrast Mode refused to turn off. Their desktop wallpaper did return, indicating that it was trying to switch out of High Contrast Mode, but not fully succeeding. Our students tend to have much of the Control Panel locked down (as I outlined above, the little bastards cherubs like to fiddle and break things), so the Control Panel applet to turn this off was not available to them, but even making it available and using the applet did not work.

I couldn’t find any mention of this via Google, and so it took me a little while to work out what was going on. I eventually traced this problem to an incorrect setting in the Registry. Here’s what it was, and how to fix it