VBA Celloffset function in For Each Cell function not work

[Junji Qian]

Hi,
Can someone help me check the below code? The first sub works, it changes the interior color of duplicate cells in selection.
However, the second one not work because of the if function.
The offset and interior condition both not work.

Thank you!
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Sub dup()
' dup Macro
    Selection.FormatConditions.AddUniqueValues
    Selection.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
    Selection.FormatConditions(1).DupeUnique = xlDuplicate
    With Selection.FormatConditions(1).Interior
        .PatternColorIndex = xlAutomatic
        .Color = 255
        .TintAndShade = 0
    End With
    Selection.FormatConditions(1).StopIfTrue = False
Call Bold
End Sub

'wrong one but right intention

Sub Bold()
For Each cell In Selection
If cell.Interior.ColorIndex = 255 Then
  cell.Offset(-4, 0).Font.Bold = True
End If
Next cell
End Sub

[SamT]

FormatCondition does not effect the Interior of Ranges. IOW, the Cells Interior Colors and ColorIndexes have not been set.

ColorIndexes can only be 1 to 56 and a couple of constants that mean no color.
Colors can be any of a few vbConstants or any RGB color code

[p45cal]

Sub dup()
     ' dup Macro
    Selection.FormatConditions.AddUniqueValues
    Selection.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
    Selection.FormatConditions(1).DupeUnique = xlDuplicate
    With Selection.FormatConditions(1).Interior
        .PatternColorIndex = xlAutomatic
        .Color = 255
        .TintAndShade = 0
    End With
    Selection.FormatConditions(1).StopIfTrue = False
    Call Bold
End Sub
Sub Bold()
For Each cell In Selection
  If cell.DisplayFormat.Interior.Color = 255 Then
    cell.Offset(-4, 0).Font.Bold = True
  End If
Next cell
End Sub

Realise that
cell.Offset(-4, 0).Font.Bold = True
boldens the cell 4 cells ABOVE the selection.
The only changes are:
If cell.DisplayFormat.Interior.Color = 255 Then

[Junji Qian]

Thank you SamT for the suggestions. I was confused by the colorindex before but now I understand.
Thanks!

[Junji Qian]

Thank you so much P45cal!!! Your code works perfectly. I can appreciate anymore