Active versus Inactive Mountain Lion Windows
To work within a OS X Mountain Lion window, the window must be active. The active window is always the frontmost window, and inactive windows always appear behind the active window. Only one window can be active at a time. To make a window active, click it anywhere — in the middle, on the title bar, or on a scroll bar. It doesn’t matter where; just click anywhere to activate it.
Here is an example of an active window in front of an inactive window (the Applications window and the Utilities window, respectively).
The following is a list of the major visual cues that distinguish active from inactive windows:
The active window’s title bar: The Close, Minimize, and Zoom buttons are red, yellow, and green. The inactive windows’ buttons are not.
This is a nice visual cue — colored items are active, and gray ones are inactive. Better still, if you move your mouse over an inactive window’s gumdrop buttons, they light up in their usual colors so you can close, minimize, or zoom an inactive window without first making it active. Neat!
Other buttons and scroll bars in an active window: They’re bright. In an inactive window, these features are grayed out and more subdued.
Bigger and darker drop shadows in an active window: They grab your attention more than those of inactive windows.