transparency as default

[Alan G Isaac <aisaac american edu>]

Today I needed to draw a diagram where
the objects were transparent (i.e.,
set property to 'draw background: No').

i. Transparency is mentioned briefly in
the docs but achieving it is not discussed.
I found the relevant dialogue by trial
and error.

ii. I could not find out how to make it
the default for new objects.  Looking in
preferences, I expected to find 'object
defaults' next to 'diagram defaults', but
it was not there.  So I had to change each
object separately.

How can I (temporarily) make this the default?

Thanks,
Alan Isaac