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
WRONG!! There is NOTHING about changing the task bar in the WINDOW color selection!
There is NO transparency box either. I am running Windows Ultimate 64 and find very few
ways of changing the look of anything. It is very limited by default. Linux OS on the other
hand is VERY customizable!! I run a dual boot set up with win7 and Linux Mint 11 and the
more I run Linux, the more I want to stay on that Operating system!