Id like to point out..
IT IS OK THAT THERE IS ONLY 16 COLOURS FOR SENNDING..
OR else MIRC would look like a [censored] rainbow!
No one wants that..
Theses Colours I request is ONLY SEEN BY THE PERSON USING THAT SINGUALR VERSION OF MIRC!
But i see now what the confusion is about, and I see why this may or may not help out there..
I think you're wrong, a lot of people want that, I've seen this being requested many times here and there (and I'm aware that I'm just discussing it again, but since you've brought the subject...). Additional colour spots (16-98) would be great.
mIRC would look like a [censored] rainbow only if its particular user wanted it to look like that. I can't see what's wrong about it. The colour values aren't shared through IRC, only the ctrl codes they associate with are. Other people would see the colours they wanted mIRC to show.
Of course, I could see a problem with people creating autocolour scripts using 30, 40 colours per message. To avoid this particular problem, my suggestion is: make additional colours local (ie. IRC messages with ctrlK+16 would still show up with the same colour as ctrlK+0, but you could use ctrlK+16's unique colour for things other than messages sent or received - for displaying purposes). If they're local, then no autocolour scripts like in the example mentioned would be possible.
mIRC theming (as in old 5.xx "efnet" scripts like opal, convex, one, etc etc) could rise from the dead if such feature existed.