I would guess that you're talking about a nick completer? Where if you type a nick with a colon after it at the beginning of a line, that nick will be formatted in some way (color, bold, underline, fancy characters around it, etc).
Here is the code:
Code:
on ^*:tabcomp:*:{
editbox -ap $+($chr(2),$1,:,$chr(2))
haltdef
}