Use a browser plugin. All major browsers have plugins/addons that can "color pick" from your screen. It will make your life a lot easier.
Background: #2F4456 --- But it does use a gradient which alters the color a bit.. (This is why a "color pick" might help unless you use the same gradient.
Gradient: /images/gradients/gradient-grey-down.png
The other thing you can do is not use the vbulletin gradient and it will match or make the logo with a transparent background.