Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Target, Range("A1")) Is Nothing Then Exit Sub
If Target.Count > 1 Then Exit Sub
If Range("A1").Value > 0 Then
Sheets(2).Tab.Color = RGB(255, 0, 0)
Else: Sheets(2).Tab.Color = RGB(0, 225, 0)
End If
End Sub