Hi Jannik,
I enhanced Mondrian with what you asked for (preferred size in presence of subviews (was existing in VW but not in Pharo), extra method for edge addition). However, I still cannot open your DSM. The reason is that FAMIX2Package does not understand color:
FAMIX2Package new color: Color blue
Again, I am not sure this is the best way to do this. Shape should be aware of colors, not the domain.
Cheers, Alexandre