Quicksilver?
http://en.wikipedia.org/wiki/Quicksilver_(software)
I don't use it though, but I do know you can use it to launch apps, among doing many other things.
And I'm guessing you can customize it, so that it would be gray/black?
[EDIT]
Waaait a second!
Are you just talking about the Application Switcher that is triggered by pressing Command Tab??
That kinda fits your description perfectly!
Application Switcher
Besides using the Dock to switch applications, you can use Application Switcher key combinations.
* Command Tab
Cycle forward through open applications. Keep the Command key pressed continuously, while pressing and releasing the Tab key as desired. Pressing it one time will switch to the previous application you were using. You can also use Command-~ (Command-tilde) to cycle backward through open applications. You can also use the mouse, arrow keys, or (if your mouse has one) scroll wheel to select an application in the Command-Tab row.
* Command Shift Tab
Cycle backward through open applications. Keep the Command key pressed continuously, while pressing and releasing the Tab and Shift keys as desired.
* Command H
Hides an application that you have selected via Application Switcher. The Command key must be held continuously from the time your selection is made until you press H. After hiding an application, you must select another via Application Switcher, or it will return to the foreground when you release Command.
* Command Q
Quit an application. This is a common key combination independent of the Dock, but it may be useful with Application Switcher.
from
http://docs.info.apple.com/article.html?artnum=106743 (at the bottom)
[edit]
Then again, there's also this one:
http://www.manytricks.com/witch/
