Do you mean for the posts themselves, or the overall background? Just so you're aware, there are two shades of gray-blue used for the individual posts, and they alternate over the course of a thread.
Using a screen-cap and Paint Shop Pro, I got the following values:
E7EAEF - darker 'post background'
F0F4F7 - lighter 'post background'
FFFFFF - overall background (which means that my monitor is probably dusty. I wasn't thinking that was white)