Right now such painting is not supported in cAlgo. The only way you can color series like this is to use PlotType.Points or PlotType.Histogram. Try this in your example:

 

[Output("Dn", Color = Colors.Magenta, PlotType = PlotType.Points)]

You will get points colored correctly. You can also draw line and that draw points on top of it to indicate up or down trend.