It would be nice if Colloquy could (optionally?) display a badge on the dock icon (similiar to Mail.app, Proteus and other apps including chat programs and rss readers) that gives an indication that there are unread messages. It would display the number of "unread" messages. The color of the badge could be used to indicate whether any of those messages are in a query (=message directed directly at the user), resp. the messages contained any highlights / the users nickname.
Conversation, another Mac OS X IRC client, implements this, see <http://homepage.mac.com/philrobin/conversation/page2.html>.