It's a good deal more than color options. check out this site. It will help you in your quest for knowlege.

http://www.sigsauer.com/Products/

The P220 and the P226 are SiG's full sized guns withing their "P" Series of handguns. The slightly compact versions of these guns are the P220 Carry and the P228/P229. FYI, THe P220 is chambered in .45, while the P226/P229 are available in 9mm/.357SIG/.40S&W. The P220 Mach and the P226 X-Five are geared and set up for competition use straight out of the box. The P220 Compact is as the name states, compact sized intended directly for those wishing something smaller for CCW or really small hands. The equivalent in the other calibers would be the P239. The Equinox and Elite pistols are just fancied up in different ways for those that are looking for that kind of distinction. The Elite has a beavertail while the Equinox does not. The DAK is the SiG refined version of a DAO action (Double Action Only) meaning that everytime you cycle the trigger, it cocks and releases the hammer. An SAO action (Single Action Only) only releases the hammer to strike the firing pin and make the gun discharge. One usually has to "rack" the slide before taking the first shot.

Any other questions? Feel free to ask. BTW, Greetings and welcome to the forum.