Just make the background black and the text white, and have a small banner (and if people complain add a [small/tiny] close button to the banner which returns the site to normal colours).
If SOPA/PIPA comes into action then sites that let users upload their own content, so that includes StackExchange sites (as StackExchange is not responsible for, nor owns, what we upload (ask/answer/comment/etc).
So posting this link would allow StackExchange to be shut down, under SOPA/PIPA.
I think 24 hours of a black background is worth being able to continue asking and answering questions for the near future. (Don't think: "Oh it's just one site it won't make a difference", because it's not 1 site, it's a whole network of over a million users (quite a bit over I'd imagine), and if everyone thought that in general, martial law would be in place years ago)
The people who complained about the banner last time had no idea, you can try to stay apolitical, but it's not about politics anymore it's about the Internet, and the survival of sites like these. Even if 300 users bother to come on Meta to complain/up-vote a complaint, that's less than 0.03% of the users on StackOverflow alone.