I currently use baseline property of the SChartLineSeries to have the gradient fill effect until the baseline, as previously suggested by you. It works perfectly for the chart that shows all data points at once, but when we need to show only a smaller range of all data at a time by setting the baseline property dynamically in the didAlterRangeOn delegate and doing the redraw, there would be problems. Here's the normal one:
And here are the two with the problems:
1) This one seems just ignore the baseline property. In the log I could read the baseline property is 22, but it doesn't work.
2) This one shows the strange red color, of which I never set elsewhere in the controller.
Thanks in advance for your help then.