Public Class Form1
    Private fenster2 As New List(Of Form2)
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        fenster2.Add(New Form2)
        fenster2(fenster2.Count - 1).Show()
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
        fenster2(CInt(TextBox1.Text)).BackColor = Color.Blue
    End Sub
End Class