I have an HP LP3065 display and a few days ago upon returning to the computer (others in the family probably had used is between my sessions) I noticed that all the colors seemed a bit subdued. This is not the case for the MacBook Air's built in screen. I am running OS X Lion. It is almost as if there was a slider between black and white and color and someone moved it closer to black and white. Could this be due to a software setting on my Mac? Or perhaps it is a hardware setting on the display? There are plus and minus buttons on the display but pressing them seems to do nothing.
Have you checked to see if the Color Profile settings have changed? Go to System Preferences, Displays, Color. Try choosing a different profile, if one isn't available for your specific monitor.