I have a 30” Cinema Display attached to my 17” MacBook Pro, and often when I return to the computer after the screensaver has kicked in, I find that my display has reverted to some default ColorSync setting rather than my calibrated, gamma 2.2 profile. The visual effect is that the screen is brighter and bluer than I’d left it.
You can fix this manually by opening the Displays section of System Preferences. This little ritual has gotten quite old though, and it finally occurred to me to do some Googling. I found this helpful blog entry that suggested the following Terminal entries:
cd /Library/ColorSync/Profiles/Displays sudo chmod 664 *
(Standard disclaimers apply any time you use the terminal, execute the sudo command, and go outside on a sunny day.)
This didn’t work for me until I also changed the permissions on the Displays directory (and the other profiles in the Profiles directory too for good measure):
cd ../ sudo chmod 664 *
So far so good—I appear to be free from the forces that seek to revert me to -blech- gamma 1.8 land.
Whenever I encounter weirdness with Apple OSs or apps, I try to report them at apple.com/feedback. Who knows if it helps, but almost all the issues I reported about my iPhone became fixes in later firmware revisions.
(Oh, and of course I realize that I could just turn the screensaver off, but I tend to leave it on with password verifications for security reasons.)