It would be great if you could allow closed shapes like rectangles, triangles, ellipses to be filled with a color.
For us it would be sufficient, if this feature would be available only through the API functions.
If additionally implementing the feature for the user interface, beside the filling color a color alpha factor should be included in the properties dialog in order to control transparency.

Besides, color alpha factors would be great to have in the general properties dialogs for all objects (including lines, ...).

Thanks for considering,
RR.