ColourUtility allows you to convert one type of colour information to another. It can convert between Web/Hex, RGB, Integer and CMYK. In addition it also provides a standard Apple colour picker from where you can pick any arbitrary colour from the colour wheel (or use the magnifying tool to grab a colour from anywhere on your screen) and get it's values. If you are involved in prepress or graphic design you can load your preferred CMYK ICC profile to get more accurate CMYK conversions
Mac OS X 10.4 PPC
Mac OS X 10.3.9
Mac OS X 10.4 Intel
Mac OS X 10.3
||Mac OS X 10.3 or later, MacOS X 10.4 of later to make use of CMYK ICC Profiles.