2
... It's okay
Well, a very common thing I have noticed with dynamic sites and PHP is the fact that people just aren't sure why certain things happen with there web pages when you stir a new css tag or edit a current one..
It's my guess that the header class/id tag for the Header of this forum category is wrapped in more than one tag, thus affecting the color to output as something you didn't expect. Try using the FireFox browser's ability to highlight and area on a page and "view source selection"
If you could, find us a way to see the CSS/Theme/Templates of your site and your newbb.
Thanks