You can do it in a shape script. By default, if you do something like this
shape main
{
rectangle(0,0,100,100);
}the rectangle is filled with the default fill colour and edged with the default border colour. If you want to change that behaviour, you can try one of the following:
shape main
{
startpath();
rectangle(0,0,100,100);
endpath();
fillpath();
}The fillpath() command will fill the rectangle with the default fill colour but not draw the border.
shape main
{
startpath();
rectangle(0,0,100,100);
endpath();
strokepath();
}The strokepath() command will draw the border with the default border colour but not fill the shape.
shape main
{
startpath();
rectangle(0,0,100,100);
endpath();
fillandstrokepath();
}The fillandstrokepath() command will draw the border and fill the shape.
You want the strokepath() version.