Here’s a Mac tip courtesy of TechPwn. If you are wondering why hidden applications don’t become translucent on the Mac OS X dock, here’s a simple workaround for you.

…there is a simple terminal command that will make the dock icons of hidden applications translucent on the dock. This tip was emailed to me so I’d like to thank “Tim”. Here is the terminal command…

defaults write com.apple.Dock showhidden -bool YES

Of course, if you’d like to revert it back to normal, just use that same code but put NO.

EDIT
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J. Angelo pointed this out in the comments below – a very important step after the ones mentioned above that I missed out:

killall Dock

This turns Dock off and on again, so you can see the effect of your recently-changed default.

Also, if you want to save on system resources, you might want to turn off Dashboard. Widgets are real memory hogs. Even the simplest widget can take up to 25MB of real memory (and more virtual memory). And that’s even if they’re hidden in the background.

defaults write com.apple.dashboard mcx-disabled -boolean YES

Then

killall Dock

If you want Dashboard again, change YES to NO.

Of course, if you don’t press F12 ever Dashboard won’t get activated. This just makes sure Dashboard never gets activated even if you accidentally hit F12.

Source: TechPwn