I suppose if you know what your doing, you could also look at the forums source code.
you can't access the forum's source code
however, I'm sure you mean to look at the HTML that was generated for one of the pages
but you don't actually have to know what you're doing
in chrome, just right click on one of the parts with the blue you want, hit "inspect element," then in the right column scroll down a bit until you find the color you were looking for
