Why is the background not being removed even though my png has a transparent background?

Question

I have a png image that has no background, with an alpha channel. Despite pawn.BackColor = Color.Transparent;, the background is still there. What is it about?

Here is my whole code:

///
namespace ludo_game
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)
        {

            board.ImageLocation = "C:\\..\board.jpg";
            board.SizeMode = PictureBoxSizeMode.StretchImage;
            board.Size = new Size(500, 500);
            List<PictureBox> bluePawns = new List<PictureBox>();
            List<PictureBox> redPawns = new List<PictureBox>();
            List<PictureBox> yellowPawns = new List<PictureBox>();
            List<PictureBox> greenPawns = new List<PictureBox>();
            LoadPawns(bluePawns, "blue", 72, 130, 360, 415);
            LoadPawns(yellowPawns, "yellow", 418, 360, 360, 415);
        }

        private void LoadPawns(List<PictureBox> pawns, string color, int x1, int x2, int y1, int y2)
        {
            for (int i = 0; i < 4; i++)
            {
                PictureBox pawn = new PictureBox();
                pawn.ImageLocation = $"C:\\..\\{color}_pawn.png";
                pawn.SizeMode = PictureBoxSizeMode.StretchImage;
                pawn.Size = new Size(10, 16);
                pawn.BackColor = Color.Transparent;
                pawns.Add(pawn);
                this.Controls.Add(pawn);
                pawn.BringToFront();
            }
            pawns[0].Location = new Point(x1, y1);
            pawns[1].Location = new Point(x2, y1);
            pawns[2].Location = new Point(x1, y2);
            pawns[3].Location = new Point(x2, y2);

        }
    }
}

Here is my sample image of pawn and what it is display: