irssi
irssi is a great irc client for unix-like operating systems.
It supports tab-completion, multiple servers, multiple windows, auto-connecting, a very handy and unobtrusive activity notifier/monitor among other things
This page says how to send colored text: http://irssi.org/?page=docs&doc=formats
There is a cool plugin so that you can block what certain people say, but still tell that they were saying something: http://www.ldx.ca/src/mute.pl
See Also
If you're on Mac OS X, you'll want to fix Terminal.app so that you can scroll through the history.