Auto Recalc Formulas with change in color index number

[westy1]

Running Excel 2007
Windows Vista

The goal is to have a VBA user defined function recalculate when any cell color is changed.

So far, I have the "Automatic" selected under the "Calculation Options".
I have added "Application.Volatile" to my VBA code. I have also tried, CTRL+ALT+SHIFT+F9,
and this successfully causes the user defined function to recalculate.

Yet, I want the formula to be recalculated each time a cell color is changed. Thanks for the help.
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Here is my VBA code:

Function SumCell_Sel(rColor As Range, rRange As Range)

Application.Volatile

Dim rCell As Range
Dim iCol As Long
Dim vResult

iCol = rColor.Interior.ColorIndex

For Each rCell In rRange
If rCell.Interior.ColorIndex = iCol Then

' if logic that ensures sum operation occurs with only numbers
If (WorksheetFunction.IsNumber(rCell)) Then
vResult = WorksheetFunction.SUM(rCell, vResult)
End If

End If
Next rCell

SumCell_Sel = vResult
End Function