Sum Cells Based On Color Index

I am trying to use a function kindly listed by Dave, that allows for a SUM to be done on cells which have a certain color index. I have modified it very slightly, but unable to set the call to it without getting errors, perhaps someone can shed some light on what i am doing wrong. Dave's original code is

Function ColorFunction(rColor As Range, rRange As Range, Optional SUM As Boolean)
Dim rCell As Range
Dim lCol As Long
Dim vResult
lCol = rColor.Interior.ColorIndex
If SUM = True Then
For Each rCell In rRange
If rCell.Interior.ColorIndex = lCol Then
vResult = WorksheetFunction.SUM(rCell,vResult)
End If
Next rCell
Else
For Each rCell In rRange
If rCell.Interior.ColorIndex = lCol Then
vResult = 1 + vResult
End If
Next rCell
End If
ColorFunction = vResult
End Function.......