MacOS X Lion introduces a new Finder Toolbar icon: Label. The toolbar item consists of a drop down menu allowing you to color/label whatever you have selected. But you don't have to use it as a drop down -- just hit the icon and whatever is selected will immediately be colored with the color shown.
You can change the color of the immediate button-press option by choosing the color (or 'No Label') with nothing selected.
[crarko adds: Nice find, and a good new addition to the Toolbar items.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2011090810451459