With Mac OS 8.5 and higher, you have the option to create custom icons that are of a higher bit depth than 8-bit (256 colors). These icons are stored in a new resource (icns). However, when the cut and paste method is used in Mac OS 8.5 and above the additional icon resources for 1-bit, 4-bit and 8-bit icons are not automatically created.
Older versions of the Mac OS do not know how to interpret the new 32-bit icon. Since the other resources are unavailable, Mac OS does the best it can to display the item, giving it a generic document icon as a placeholder.
To work around this issue:
- Use an icon editing utility to create a full icon suite of bit depths for the item instead of using cut & paste from the Finder.
- Mount the item from a client running an OS older than 8.5 and cut and paste an 8-bit custom icon from the client.