Love the new sig Bomps, and incredibly timely for me to read, actually

Are you just using the default SMF theme? Because if you've changed anything then the pieces of theme that you got will overwrite the defaults. It's weird how it works ... If there is an overriding file for a particular theme, then that is chosen over the default. That's why you can have a theme that only changes the home page and nothing else.
The way that I find the thing I want to change is to change to color of it. So I'll roll through the entire Style sheet for a theme and change the color/background color of EVERYTHING to make sure that I've collected the thing I want, then start uncoloring things until I locate the ID/class I need to affect.
But I'm afraid that I don't know off the top of my head. If it gives you more than a little bit of trouble ping back and I'll find the little bastard.