What can we do to make ScottPlot better?
A clear and concise description of what we can improve would be helpful.

Can ScottPlot plot this kind figure?Only positive part is filled? Or two parts filled with different color?

Check the ScottPlot Roadmap to see if your feature is already planned for an upcoming release:
https://github.com/swharden/ScottPlot/blob/master/dev/roadmap.md