I've noticed I often do not spot an active program for a while, especially when I'm running quite a few applications at the same time. To make this distinction more clear than the small dot, Im trying to find a way to dim the unactive Dock icons, or make them black/white. So far I havn't been able to come up with a solution, though.
Now I've noticed that Adium changes its Dock icon when it's active or inactive. Perhaps this would be a nice stepping stone – how does Adium handle this?
EDIT: I went through the Adium sources, but they call [[NSApplication sharedApplication] setApplicationIconImage:image]; to change the icon. Their default is the sleeping bird and they update it at runtime from their application. Seems an impossible solution for closed-source applications, unfortunately.
Best Answer
I don't know how to dim inactive icons in the Dock. However, some people prefer the old-style two-dimensional dock that you can activate. It's certainly easier to discern which apps are open on this view.
To activate the 2D dock, open Terminal. Then type in the following command:
From there, you can log off & back on, and your Dock will have changed. If you ever need to revert this setting back run the above command again, but change the word YES for NO.