Dell U2713HM with Mac OS X, gamma caveat.
There is «Gamma» setting in monitor on screen menu:
Menu -> Color Settings -> Gamma -> PC/MAC
If you think that on Mac OS X you need simply use MAC option you wrong.
Gamma is a numerical value that describes the relationship between the varying levels of brightness or luminance that a monitor can display …
… Mac OS X v10.6 Snow Leopard uses a gamma value of 2.2 by default. In versions of Mac OS X prior to 10.6, the default system gamma value was 1.8.
In most computer systems, images are decoded with a gamma of 2.2
In case of Dell settings «PC» option is match 2.2 and «MAC» option - 1.8 value.
So for Microsoft Windows and the rest of the world «PC» option is fine.
For Mac OS X 10.5 (Leopard) and earlier you must use «MAC» option (1.8).
For Mac OS X 10.6 (Snow Leopard) and later use «PC» option (2.2).