Be aware that OSX introduces a feature in the "Universal Access" utility that can severely limit the performance of your monitor.  To review this feature proceed as follows:

Universal Access is not a "Contrast Control" for Mac LCD monitors that lack a physical control for contrast!

It should be noted that Universal Access is designed for Mac users with visual challenges, such as the need to greatly increase contrast to be able to read a text document. While this feature is very important for computer users with less than ideal vision, any use of this feature will render colors incorrect. Here's how to ensure you don't harm the color with an improper setting.

• Click on the Apple icon (top-left) then on "System Preferences"

• Next, click on the "Universal Access" icon (bottom-right).

• Ensure that the "Seeing" tab is selected.

• Under "Display", ensure that the "Enhance Contrast" slider is as far left as possible - this is the normal position. 

If the slider is positioned even a small fraction of an inch from the left, there will be a loss of shadow contrast that can hide subtle shadow details in your images.