Analysis of information sources in references of the Wikipedia article "Label (Mac OS)" in English language version.
Mac OS X 10.3 Panther: Arrived in the fall of 2003, Panther integrated Apple-branded cloud storage support for the first time, via iDisk. The Finder added a sidebar, which is a handy place to store familiar folders to this day, and colored labels for files.
XRay can also create Unix symbolic links and assign colored labels to files (an OS 9 feature not included in OS X).
Miss being able to color-code your files like you could in Mac OS 9? Unsanity LLC has released a new OS X 'haxie' called Labels X 1.0. The software enables you to add various color tints to file icons, adding the ability to sort the files by label as well (it adds a 'Label' column to the Finder list view).
You'll really miss only a handful of discarded Mac OS 9 features, like the Labels menu (for quickly categorizing your files) ...