Option Explicit
Sub En_rouge_si_aaaa_trouvé()
Dim o As Integer
Dim i As Long
Application.ScreenUpdating = False
For o = 4 To Sheets.Count
Sheets(o).Select
For i = 2 To Range("aa65536").End(xlUp).Row
If Range("aa" & i).Value = "aaaa" Then Range("aa" & i).EntireRow.Interior.ColorIndex = 3
Next i
Next o
Application.ScreenUpdating = True
End Sub