ChartSeries.ChartOptionsIndex Property
Index to the ChartOptions object that applies to this series. Note that in xlsx charts, this is the number of subchart where the series is. So when setting series, you don't need to specify the ChartOptionIndex: FlexCel will use the number of subchart no matter what you specify here.
Syntax
Namespace: FlexCel.Core
public Int32 ChartOptionsIndex { get; set; }