Option Explicit
Sub Colorer_si()
Dim c As Range
For Each c In Range("c2:c" & Range("a65535").End(xlUp).Row)
If c.Interior.ColorIndex = 38 Then c.Interior.ColorIndex = xlNone
If c <> "" Then
If c.Offset(, -1) = "Samedi" Or c.Offset(, -1) = "Dimanche" Then c.Interior.ColorIndex = 38
End If
Next
End Sub