formule reherche de doublon

Private Sub Worksheet_Change(ByVal Target As Range)
Dim c As Range, cel As Range, Zone As Range, prem As String
  [A:A].Interior.ColorIndex = xlNone
  Set Zone = Range("A1:A" & Range("A65536").End(xlUp).Row)
    For Each cel In Zone
        Set c = Zone.Find(what:=cel, LookIn:=xlValues, LookAt:=xlWhole)
        prem = cel.Address
        Do While Not c Is Nothing And c.Address <> prem
            c.Interior.ColorIndex = 3
            cel.Interior.ColorIndex = 3
            Set c = Zone.FindNext(c)
        Loop
    Next cel
End Sub

Private Sub Worksheet_Change(ByVal Target As Range)
Dim c As Range
  [A:A].Interior.ColorIndex = xlNone
  Set c = Range("A1")
    Do While c <> ""
        If Evaluate("Countif(A:A," & c & ")") > 1 Then c.Interior.ColorIndex = 3
    Set c = c(2, 1)
    Loop
End Sub