Possible to make this add-on?

I've got an idea for an add-on I would like to make for a chat program, but I'm not sure it's possible.

It would be a fader, where the user enters in text and the fader changes each character from one colour to another etc. Would it be possible to do this without the user having to type the text into my program, but they can just type into the original chat program and have it fade the text?

I was thinking of trying to intercept the text from the inputbox when the user presses enter, possibly by hooking which I've never done before, so I'm not sure hooking would be what's needed. My program would then fade it and send it back to be displayed for everyone to see.

I can do this when the user types into my program, then it sends the formatted text along with an enter key press, into the chat programs inputbox. I was just wondering if it's possible to do it without the user typing into a seperate form.

I hope I've explained it well enough, if not, just ask me to clarify :) . Any help with this would be appreciated. I'm already half expecting it not to be possible anyway, at least with VB.

Thanks :)

No one has any ideas? Even if it's not possible, I'd still like to know, so then I can stop wasting my time trying to work out how to do it.

Thanks to anyone who can help :)