程序代码：

using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace TransColorControl
{
    public sealed partial class CControl : Control
    {
        #region 构造函数

        public CControl()
        {
            InitializeComponent();

            SetStyle(ControlStyles.SupportsTransparentBackColor | ControlStyles.UserPaint
                     | ControlStyles.AllPaintingInWmPaint | ControlStyles.Opaque, true);
        }

        #endregion

        #region 重写属性

        protected override CreateParams CreateParams
        {
            get
            {
                var result = base.CreateParams;
                result.ExStyle |= 0x00000020;
                return result;
            }
        }

        #endregion

        #region 重写方法

        protected override void OnPaint(PaintEventArgs pe)
        {
            base.OnPaint(pe);
            pe.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
            pe.Graphics.FillPie(new SolidBrush(Color.Blue), 0, 0, 30, 30, 0, 270);
        }

        #endregion
    }
}