VBA - Formatting Points On A Chart

I'm trying to write a macro that will format my chart data based on the corresponding cell value. I have the following code, which runs without error, but the formatting on data points doesn't change. I can't seem to get this to actually change the color of the data point in the chart.

Code:
Sub FormatChart()
Dim wb As Workbook
Dim ws As Worksheet
Dim wks As Worksheet
Dim y As Long
Dim j As Long

'this routine will format the charts on worksheets "SL11730" & "SL14100" 'so that data points equal to or above 98% will be green filled and 'all other points will be red filled

'set loop counter to two (contract (4100) & retail (1730))
j = 1
'start loop
Do Until j = 3
If j = 1 Then strwkb = "SL11730"
If j = 2 Then strwkb = "SL14100"

[code].....