comboBox加载颜色下拉列表框

在comboBox中，实现自定义加载项需要设定以下俩个内容。
1，comboBox1.DrawMode=OwerDrawFixed;  //即设定组合框的加载方式为手动加载。
2，重写comboBox的Draw_Item事件。
private void Form1_Load(object sender, EventArgs e)
         {
                       Array allColors = Enum.GetValues(typeof(KnownColor)); //获得系统颜色集合                                                    
             foreach (KnownColor var in allColors)  //KnownColor是一种枚举类型，包括了系统的所有颜色
             {
                 myComboBox.Items.Add(var.ToString());  //加载该选项框的子项
             }
                    }
         private void myComboBox_DrawItem(object sender, DrawItemEventArgs e)
         {
             //判断是否需要重绘
             if (e.Index >= 0)
             {
                 string colorName = myComboBox.Items[e.Index].ToString();  //子项的颜色名
                 SolidBrush brush = new SolidBrush(Color.FromName(colorName)); //画笔
                 Font font = new Font("宋体", 9);                                                       //字体样式
                               Rectangle rect = e.Bounds;                                                               //获得需要重绘的区域
                 rect.Inflate(-2, -2);                                                                                           Rectangle rectColor = new Rectangle(rect.Location,new Size(20,rect.Height));
                 e.Graphics.FillRectangle(brush, rectColor);                                                  // 填充颜色  
                 e.Graphics.DrawRectangle(Pens.Black, rectColor);                                       // 绘制边框                 //绘制文字
                 e.Graphics.DrawString(colorName, font, brushs, (rect.X+22), rect.Y);
                  
               //绘制选中效果
                 if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
                 {
                     SolidBrush brushItem = new SolidBrush(SystemColors.MenuHighlight); //画笔
                     Rectangle rectItem = e.Bounds;
                     e.Graphics.FillRectangle(brushItem, rectItem);
                 }
                 else
                 {
                     SolidBrush brushItem = new SolidBrush(SystemColors.Window); //画笔
                     Rectangle rectItem = e.Bounds;
                     e.Graphics.FillRectangle(brushItem, rectItem);