MacOS – How to make the dock transparent in Mountain Lion

The easiest way would be the following:

1. Download, install and update the free Server Admin Tools from Apple.
2. If you´re currently logged into the Guest User Account, log out. Open /Applications/Server/Workgroup Manager and connect to Address: localhost with the username and password of your admin user
3. Ignore the warning message about working on a local configuration, then go into the menu "View" and select "Show System Records".
4. On the left hand side, select the Guest-User and in the window titlebar click on "Preferences"
5. Click Dock on the right side. Select "Manage Always" at the top of the window and then add and remove the Dock items you want in your customized Dock. Uncheck the checkbox "Merge With User's Dock" at the bottom of the window. Click on "Apply Now" and log in as the Guest User to see it in effect.

You would most likely need to use a translucent/transparent background image to accomplish what you're asking. If you know how to make an image 90% transparent then you should be able to experiment and to come up with something similar. Tweaking the UI is art in many ways, however, it's not necessarily a function of the interface creating the effect; the elements that compose it (background color, wallpaper, dock and icons) play a key role.

[posted for reference]

System Preferences > Desktop & Screen Saver > Translucent menu bar

• One app that I've used to achieve a similar effect is called Nocturne. I'm unsure of it's compatibility with Lion though.