I wrote a user-defined function that sums all cells in a given range that
have the same color fill as the calling cell. The code works great except
when the user changes the fill color of a cell. The formula will not update
because technically no values changed.

How can I get around this?

I am providing the code for others to use.

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Function sumColor(range1 As Range, Optional range2 As Range, Optional range3
As Range, Optional range4 As Range)

sumColor = 0

For Each cell In range1
If cell.Interior.ColorIndex = Application.ThisCell.Interior.ColorIndex
Then
sumColor = sumColor + cell.Value
End If
Next cell

If Not range2 Is Nothing Then
For Each cell In range2
If cell.Interior.ColorIndex =
Application.ThisCell.Interior.ColorIndex Then
sumColor = sumColor + cell.Value
End If
Next cell
End If

If Not range3 Is Nothing Then
For Each cell In range3
If cell.Interior.ColorIndex =
Application.ThisCell.Interior.ColorIndex Then
sumColor = sumColor + cell.Value
End If
Next cell
End If

If Not range4 Is Nothing Then
For Each cell In range4
If cell.Interior.ColorIndex =
Application.ThisCell.Interior.ColorIndex Then
sumColor = sumColor + cell.Value
End If
Next cell
End If

End Function
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Thanks, Pflugs