eta: If you wanna change the colour of the highlighting, just change the colour in the trigger.
One complaint I've found a lot of in Achaea, is that we don't have says colouring for emotes, or emotes appearing in gmcp.Comm module like other games do (not yet, at least! *hint hint*)
Well, now you can have it! At least client-side, anyway. Unfortunately it highlights stuff in more places than just emotes (namely help files with quotes in them, I should have eliminated them from other sources though, like CT etc)
One pre-requisite is that you're using something (whether it be some form of tabbed chat or whatever) which enables the gmcp.Comm module, otherwise it'll highlight stuff in ct etc as well. If you don't have either of those, simply add this to your login trigger:
sendGMCP('Core.Supports.Add ["Comm.Channel 1"]')