Option to fill the area below the line

[jojost1]

For a look similar to https://github.com/pichukov/LightChart and https://github.com/AppPear/ChartView for example, I really like that look 😄

Optionally give an option to provide two colors to display a gradient, similar to lineSecondColor.

[Jonathan-Gander]

This one is difficult. I am open for some help 😉

[smotched]

Might be able to work on this one 🙂