NETでラベルの背景を透かせる問題点を教えて

using System;
using System.Drawing;
using System.Windows.Forms;

class Form1 : Form {
    [STAThread]
    static void Main() {
        Application.Run(new Form1());
    }

    Form1() {
        ClientSize = new System.Drawing.Size(712, 405);

        PictureBox p = new PictureBox();
        p.Image = Image.FromFile(@"c:\windows\system32\setup.bmp");
        p.Location = new Point(192, 80);
        p.Size = new Size(368, 256);
        p.SizeMode = PictureBoxSizeMode.StretchImage;
        Controls.Add(p);
        
        Label l = new Label();
        l.Text = "Hello World!";
        l.Font = new Font("Tahoma", 48F, FontStyle.Regular, GraphicsUnit.Point, (byte)128);
        l.Size = new Size(232, 200);
        l.ForeColor = Color.Red;
        l.BackColor = Color.Transparent;
        Controls.Add(l);
        
        l.Parent = p;
    }
}