🚀 go-pugleaf

I have a question about icons...

I created an icon using Dpaint and iff2icon.  It worked fine, except
the background color (blue if you use default workbench colors) is not
transparent.  When you select the icon and drag it around, it drags around
this big blue square which obscures everything behind it.  I notice that
some icons are like this, and some are not.  I searched the definitions
of the data structures which make up an icon 
(actuall a DiskObject), but
couldn't find any flag which would seem to control this.


Anyone know what it is that makes some icons have transparent backgrounds, 
and others not?

Thanks,
Duncan Thomson