Repèrer les doubles

Sub test()
    Dim i, j, dl, NRef
    dl = Range("D65536").End(xlUp).Row
    For j = 2 To dl - 1
        If Cells(j, 4) <> "" Then
            NRef = Cells(j, 4)
            For i = j + 1 To dl
                If NRef = Cells(i, 4) Then
                    Cells(j, 4).Interior.Color = vbBlack
                    Cells(j, 4).Font.Color = vbRed
                    Cells(i, 4).Interior.Color = vbBlack
                    Cells(i, 4).Font.Color = vbRed
                End If
            Next
        End If
    Next
End Sub