The “Skin” pane :

This pane lets you setup the appearance of A-Dock

Using the Mac OS appearance

By default, A-Dock will use the look of Mac OS. Whether you use a theme or a Kaleidoscope scheme, A-Dock will use that look.

Using a skin

However, you can customize further A-Dock's look by selecting a skin. The built-in skin of A-Dock is QuickTime 4, but 4 other skins are provided as separate files and all the documentation to build your own skin is available.

If you choose an alternate skin, then you have to select it by clicking on the “Choose Skin” button. An open dialog will ask you to locate the skin's file on your hard drive.

Important :
If you're using an alternate skin, A-Dock will load it at startup (or when you select a new skin in A-Dock Control). Thus this file HAS to be on your hard drive all the time.
Moreover, if you're in a multi-user environment, the skin has to be available to every user. Thus I would recommend putting skin files in the Application Support Folder of your System Folder.