This could be done via how the browsers do it, say ^k#ff8d8t then mIRC could internally interpret the colorcode from that to display the text in that color within other mIRC clients.
No-- this would not be backwards compatible. This would break mIRC users as well.
Other clients would just simply show #ff8d8t as apposed to the actual color, so it would not break other IRC Clients, unless they standardized the colorcode format across their irc clients.
Not properly displaying a colour is the definition of breaking a client. The idea that a client is not "broken" because it falls back to displaying regular text isn't exactly a good argument on a text-based protocol. This was the same argument made by MS Comic Chat, but that only led to the client getting kicked from every channel because nobody else could parse the gibberish coming from those users. It's just not a good experience for other clients.
