Excel chart comexception was unhandled - invalid parameter

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C#

oRange = (Excel.Range)oSheet.Range[oSheet.Cells[2, ypColumn], oSheet.Cells[12, ypColumn]];
                  Chart1.SetSourceData(oRange, Type.Missing);

                  //Set the Chart Title
                  Chart1.HasTitle = true;
                  Chart1.ChartTitle.Text = "B2 +/- 5 lots Yield Trend (%)";

                  //Set the y-axis

                  var B2yaxis = (Excel.Axis)Chart1.Axes(Excel.XlAxisType.xlValue, Excel.XlAxisGroup.xlPrimary);
                  B2yaxis.HasTitle = true;
                  B2yaxis.AxisTitle.Text = "Yield Percentage";

                  //Vertical Allignment of y-axis title

                  B2yaxis.AxisTitle.Orientation = Excel.XlOrientation.xlVertical;

                  //Set the X-axis
                  var B2xaxis = (Excel.Axis)Chart1.Axes(Excel.XlAxisType.xlCategory, Excel.XlAxisGroup.xlPrimary);
                  B2xaxis.HasTitle = true;
                  B2xaxis.AxisTitle.Text = "Lot Number";

                  Excel.SeriesCollection seriescollectionB2 = Chart1.SeriesCollection();
                  Excel.Series B2series1 = seriescollectionB2.NewSeries();
                  B2series1.XValues = oSheet.get_Range("B2", "B15");

                  Excel.SeriesCollection addseriescollectionB2 = Chart1.SeriesCollection();
                  Excel.Series B2series2 = addseriescollectionB2.NewSeries();
                  B2series2.XValues = oSheet.get_Range("B7", Type.Missing);


                  //Horizonal Allignment of x-axis title
                  B2xaxis.AxisTitle.Orientation = Excel.XlOrientation.xlHorizontal;

                  //Setting colour of chart
                  int c = 6;
                  B2series1.Points(c).Color = (int)Excel.XlRgbColor.rgbRed;

Hi all. I have this code to plot a graph on Excel, using C#. I created an Excel series. I want to change the color of a particular point in that series.
However, I'm getting an error of "COMException was unhandled - Invalid Parameter" at the line

B2series.Points(c).Color = (int)Excel.XlRgbColor.rgbRed

I have no idea how to change the code. Any help will be greatly appreciated. Thank you!

What I have tried:

I've tried adding references, and even changing the code to

B2series.Points(c).Color = System.Drawing.Color.Red