Sub Farben()
Dim i As Long, Farbe(2) As Byte
    Farbe(0) = 41
    Farbe(1) = 33
    Rows("1:1").Interior.ColorIndex = Farbe(0)
    For i = 2 To 50
        If Range("A" & i - 1) = Range("A" & i) Then
            Rows(i & ":" & i).Interior.ColorIndex = Farbe(0)
        Else
            Rows(i & ":" & i).Interior.ColorIndex = Farbe(1)
            Farbe(2) = Farbe(0)
            Farbe(0) = Farbe(1)
            Farbe(1) = Farbe(2)
        End If
    Next i
End Sub