How to Use CMYK Working Spaces in Photoshop CS6
When you choose one of the predefined color settings in Adobe Photoshop Creative Suite 6, those colors settings become your working spaces. Working spaces are the color profiles associated with the color modes. The custom color setting requires you choose your own working spaces.
CMYK working spaces are a little more involved than RGB options. CMYK working spaces serve a threefold purpose:
Photoshop converts your RGB file to the CMYK color space when you choose Image→Mode→CMYK.
You view your RGB image in the CMYK color space when you choose View→Proof Setup→Working CMYK.
The CMYK color space determines how a CMYK file is displayed on an RGB monitor.
Europe (FOGRA), Japan, and the United States have specific color profiles for printing. Those CMYK options are divided between those for coated and uncoated paper, and sheet-fed or web printing presses.
The latter two have different percentages of ink coverage and paper stock. The GRACol profile (General Requirements for Applications in Commercial Offset Lithography) provides press measurement data to be used to create profiles for sheetfed offset printing. Macs also have a ColorSync Generic CMYK profile. You should leave the setting at U.S. web Coated (SWOP) v2 unless your commercial printer tells you otherwise.