I'm testing your library again after some time and I'm having an issue with overlapping SplineArea series in a Scatter Series Descriptor.
I'm attaching a screenshot of what I get.
As you can see, in the right side there are two overlapping splines, and I'd expect them to be drawn like two separate objects, so that the only way to distinguish between them would be increasing border's thickness.
Is there a way to do it and maybe make palette's colors a little bit transparen? (I've added a second attachment with a quick example made with Paint)