Labels X by Unsanity:
Labels X adds file labeling features into Mac OS X. This means, you can apply various color tints to file icons, and sort the files by label.
This gives you more freedom and options in organizing your files. Additionally, Labels X shares file label information with Mac OS 9, so no matter, where you
label your files - you will see the labels in both Mac OS 9 and Mac OS X (file labeling is a built-in feature in Mac OS 9).
Looks like they’ve done a great job. Having not used MacOS 9 for a few years, Finder labels now feel really old-school (in a good way).