CSS Changes to Blogs.MU - Specifically the Dark Top Half of Page and All Menu CSS

I searched but could not find the answer in the forums. Please feel free to direct me if the answer exists elsewhere.

Running a Multisite with BuddyPress 1.2.7 on WP 3.0.5 and trying out the Blogs.MU theme.

By default, in Blogs.MU there is a blackish background color above the navigation menu and an image behind the Network intro header. I want to change that color and image as well as all navigation menu colors (bg, link, hover, etc.) but I haven't found this option anywhere in the user interface I haven't been able to locate the code in the theme files.

If there is no way to change this in the user interface, please direct me toward the appropriate stylesheet(s) and I (hopefully) can get it from there.

Thank you!