Option Explicit
Sub Police_couleur_noire_si_doublon()
Dim c As Range
With Application: .ScreenUpdating = False: .Calculation = xlManual: .EnableEvents = False: End With
Columns(1).Insert
Range("a5:a" & Cells(Rows.Count, 3).End(xlUp).Row).FormulaR1C1 = "=COUNTIF(C[3],Tableau85[@Commande])"
For Each c In Columns("A:A").SpecialCells(xlCellTypeFormulas, 1)
If c > 0 Then c.Offset(, 14).Font.ColorIndex = 1
Next
Columns(1).Delete
With Application: .EnableEvents = True: .Calculation = xlAutomatic: .ScreenUpdating = True: End With
End Sub