Have you calibrated the display yet?
Directions:
Using the Display Calibrator Assistant in Mac OS X:
From the Apple menu, choose System Preferences.
Click Displays.
Click the Color tab.
Click the Calibrate button.
Click on the Expert Mode checkbox.
Follow the instructions, and save the custom profile when finished.
Or you could try,
SuperCal It's what I use and it's free to try.
SuperCal is shareware which means that you can download it and try it out for free, but it will have some features disabled until it a license is purchased and activated. This lets you see the on-screen results of SuperCal's calibration before needing to purchase a license.
Hope that helps