I find it quite annoying that I can have a certain theme on my profile, but in topics everybody see's my posts in the theme they've chosen to view the rest of the site in,
so my suggestion is that in any topic, each post made by me for example, will have the purple theme on it, for everyone.

Pros:
It can match ur Sig, if u have a colormatching one that is.
People would most likely spend some more time enhancing their profile/sig.

Cons:
Damn colorful topics.(Not really a con is it)

I personally would prefer not to have rainbow topics all over the boards, I choose the setting I have because it's easy on my eyes.
it would be a headache to have no control over how I view the board.

Perhaps add an *option to show board as default or as in themes chosen.

I agree with Josh and in my opinion, having so many colors would be distracting and they would make for a very ugly looking forum. You can already set to see the whole board in whatever style you'd like, so just use the one that matches your signature. I know you're wanting a bit more liberty to personalize your account for others to see, but I think the orbs fulfill this enough and they are small enough to not be distracting.

I vote no even with your addition to it being optional since I feel very few people would actually use it. By the way, attach a poll to your topic so that we can see how many people would like this or not.

1. nope i don't want to have rainbow topics. this would made spamming much more horrible tho
2. your sig doen't match the jsp rules better make new one