It'd be nice to force colors on all incoming IMs. The other person would not even notice, since you could just mess with it locally. You could also have your own messages set up with your custom font while the other person sees it as white background with black text.
That would be a nice feature to use on buddies who use horrible background colors with weird font colors that make it hard to read what they're saying :).
(i found this thread because i was going to suggest the same thing, but using the search feature found that someone already posted it. )
yes yes please please do the font/color over-ride thing. i talk to a lot of people on AIM who unfortunatly have no sense of what is a readable font/color selection. we all love girls, but not so much when i have to squint at their pink on purple color scheme. i'd LOVE to make it so all i see is black arial on a white background.