judsonarq:
I don't think the pen for the background fill of a Fragment (a fill drawn in the 2D Symbol window) can be parametric, only the foreground pen and fill type can be controlled. So you will need to use the
POLY2_B command in the 2D Script to numerically define the fill and have control over its background pen.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David