this.Padding = new System.Windows.Forms.Padding(3, 3, 3, 3);

protected override void OnPaintBackground(PaintEventArgs e)
{
    //base.OnPaintBackground(e);  //comment this out to prevent default painting
    using (SolidBrush brush = new SolidBrush(Color.Purple))  //any color you like
        e.Graphics.FillRectangle(brush, e.ClipRectangle);
}