Making the Mac Dock Icons Transparent
Hiding an application in Mac helps keep your desktop organized. A hidden application is open in the background but not visible on the desktop. A hidden app has an icon on the Dock. Clicking the Dock icon brings the app back onto the desktop.
You can hide an application by pressing Command+H when you are in the app. Alternatively, you can click on the application’s name on the menu bar at the top left of the desktop and choose Hide from the dropdown menu.
By default in OS X, you can't tell a hidden application icon from a normal Dock icon. However, you can distinguish which Dock apps are open but hidden by turning on a switch in the operating system that makes hidden Dock icons transparent. Any icons on the Dock that are solid are closed apps that are normally found on the Dock whether they are open or not. Follow the steps below to enter a command line in Terminal to turn on this feature.
Open Finder and browse to the Applications folder. Open the Utilities folder under that. Find and double-click the Terminal app to open it.
Enter the following line in the Terminal:
defaults write com.apple.Dock showhidden -bool YES
Refresh the Dock by entering the following line in Terminal:
The Dock will disappear briefly and reappear with the feature turned on. Close the Terminal and you’re done.
Now, when you see the Dock, you will know that the transparent icons are open apps and the solid color ones are closed.