Hi
If I have interpreted you post correctly, then you have named 65,000 plus cells ?
If so, then there are better ways of spending your time !!??
I did have a thought though, If you are familiar with VBA (?), you could try pasting this into the "modified data" sheet module.
Code:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim cel As Range
For Each cel In Target
If cel = Sheets("original data").Range(cel.Address) Then
cel.Interior.ColorIndex = xlNone
Else
cel.Interior.ColorIndex = 36
End If
Next cel
End Sub
This assumes that the "original data" worksheet is named "original data" an is totally based on "the value in the same cell" indicated in you post.
The formatting of the cells would, of course, be your choice.
Is that any help !!??
MTB