[pstricks] How can I make a double line with no color in between?

[Luis Sequeira]

Hi

I am trying to connect two nodes using doubleline:
   
   \ncline[doubleline]{A}{B}

It connects the two nodes as expected.
It draws the lines in black and the space between the two lines in white, which works fine in an article.

I know that this can be changed, e.g., 

      \ncline[doubleline,doublecolor=blue]{A}{B}

draws the space between the two lines in blue. But I am doing a beamer presentation and I would like this in-between space to just be transparent.
I tried fillstyle=none, but that does not work. I tried opacity=0 and that does not work. Is there any way to do a double line without filling?


TIA 

Luís Sequeira