Right click an empty spot on the Desktop and choose Personalize. Look for the Window Color choice.
Choose the gray Slate color, uncheck the Transparency box, and slide the Intensity slider to the far right.
You can use the Color mixer options to get the colors as close to black as possible. And Save Changes.
It's not true black, but should be close enough.
I've seen a custom theme or two that are nearly identical to the Vista default.
And you can build a custom theme to suit your tastes. Create A Theme