
(Image from Mac OS X Character Viewer. I take no credit for the info in the image.)
On Mac OS X, I think Lion and above. Testing in TextEdit reveals that it is unaffected by font, as the Character Viewer appears to state in the font variation section of its entry.
Speculating on why your colleague used it, it's relatively simple to insert on Mac, using the Character Viewer/Special Characters under the emoji section (funny enough, this one's not in Messages' list of smileys). It's also easy to insert on iPad, using the Emoji "international" keyboard. There are definitely other ways to do it, and on other platforms, those are just the ways I've found to type them that aren't too hard to find. Who can't resist typing fancy colored emoticons that they found looking through random features of their system?
It might be something interesting to ask your colleague about.

This is what inspired me to make this post. Just noticed it randomly. It isn't rendered in the web page, just the tab title and the tab's hovertext. (this is on Mac 10.8 with Chrome 23)