goal_expansion

I would very much like to see a simple example of the use of goal_expansion.

I have a large program, and I would like to make a series of changes.   
I see that I am following the same pattern each time, and if I were  
writing in another language I would consider creating a macro.

This may be the wrong technique to use in Prolog, but I'm curious if it
would be possible.

For example:  A list is passed to a predicate, and the list is checked  
for an optional member (may or may not be there).  If the member is in  
the list, we use it.  If not, a default value is used.

Writing the code by hand I might do:

    (
       \+ member(color:Color, List) ->
              random_color(Color)
        ;
              true
    ),


I am wondering if I can clean that up to something more readable via
goal expansion.

(This may be a dumb way to go about things, but I would rather not rewrite
  a huge chunk of existing code)

Thanks,
Jonathon Doran