mirc should probably comply to what other clients have been doing for quite a while
And while we're at it, maybe Colloquy should comply with what mIRC has been doing for even longer. As mentioned, the reverse control code has been available as ASCII 22 for roughly a decade, yet Colloquy chose to use this character for italics. This is technically a separate issue, but it's very closely related. It's likely that mIRC had to choose ASCII 29 for italics because ASCII 22 was already in use. If Colloquy had been compliant with what mIRC has been doing for a decade now, then it would not be using a control code for italics that was already in use for something else.
I can't speak for the behaviour of other clients, but as I recall, Ircle was the only client to implement control codes prior to mIRC, so mIRC has been doing this since
before what Colloquy defines as "forever". I could be wrong here, and please point out if I am, but I'm pretty sure ASCII 22 was in use for reverse before any client had implemented support for italics, which made it reserved in this defacto-standard world of IRC we live in. Colloquy need not support reverse, but it should recognize its existence and select a more appropriate control code for italics.
Edit: For reference, mIRC added initial support for reverse at the same time support for bold and colours were first added; mIRC 4.7 in 1996:
91.Added support for bold/underline/reverse characters. Can
use Ctrl-B,U,R to insert these characters into an editbox.
