Option Explicit
Private Sub Worksheet_Change(ByVal c As Range)
If c.Column <= 3 Then
Range("a4:b13").Interior.ColorIndex = xlNone
If Application.WorksheetFunction.CountA(Range("a4:b13")) = 0 Then _
Range("a3").Interior.ColorIndex = 43 Else Range("a3").Interior.ColorIndex = 3
End If
End Sub