Private Sub Worksheet_Change(ByVal Target As Range)
If Range("A1").Interior.ColorIndex = 6 Then Range("C1").Value = Range("C1").Value * 2
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Not Application.Intersect(Target, [C1]) Is Nothing Then
If Range("A1").Interior.ColorIndex = 6 Then Target.Value = Target.Value * 2
End If
End Sub