I have had this issue once while I installed the 10.6.5 upgrade, shortly before it was done and shutting down.
Apple has acknowledged issues and say they will be fixed through an upcoming software fix. It only affects one display panel type as far as I know. Putting the computer into standby, and waking it up again should fix the issue temporarily.
Can you look up your panel type and post it here, please? Apple menu -> System preferences -> Displays -> Color -> Open Profile -> scroll way down -> click the last entry -> post the value of the model line
I will compare it to the display model of the MacBook Air I have seen this on tomorrow and report if it's a match.