From Synfig Studio :: Documentation
Invert is a boolean property that applies to the following Layers:
This parameter inverts the filling of the shape to the outside part of its contour when checked on. Its default value is checked off (shape looks as usual).
A sample of Invert Parameter set to off:
A sample of Invert Parameter set to on:
You can download the sif used in this page File:Invert Parameter.sifz