[Ipstenu (Mika Epstein)]

I’m either looking for something like that, or alternately jury-rigging a custom tag (if that’s even possible) to let my users post, say, black text on a black background (in a blockquote box) that you have to highlight to see.

Okay I can’t sort out the javascript stuff, but I can make a spoiler bar: Spoiler Tags Plugin

It’s working as intended on my forums right now.