C#DataGridView单元格边框颜色问题

表头单元格：

/// <summary>
    /// 表格列头部单元格
    /// </summary>
    public class DataGridViewColorColumnHeaderCell : DataGridViewColumnHeaderCell
    {
        /// <summary>
        /// 顶部边框颜色
        /// </summary>
        public Color TopBorderColor
        {
            get;
            set;
        }
        /// <summary>
        /// 右侧边框颜色
        /// </summary>
        public Color RightBorderColor
        {
            get;
            set;
        }
        /// <summary>
        /// 下部边框颜色
        /// </summary>
        public Color BottomBorderColor
        {
            get;
            set;
        }
        /// <summary>
        /// 左侧边框颜色
        /// </summary>
        public Color LeftBorderColor
        {
            get;
            set;
        }

        // Override the Clone method so that the Enabled property is copied.
        public override object Clone()
        {
            DataGridViewColorColumnHeaderCell cell =
                (DataGridViewColorColumnHeaderCell)base.Clone();
            cell.TopBorderColor = this.TopBorderColor;
            cell.RightBorderColor = this.RightBorderColor;
            cell.BottomBorderColor = this.BottomBorderColor;
            cell.LeftBorderColor = this.LeftBorderColor;
            return cell;
        }

        // By default, enable the button cell.
        public DataGridViewColorColumnHeaderCell()
        {
            this.TopBorderColor = Color.Empty;
            this.RightBorderColor = Color.Empty;
            this.BottomBorderColor = Color.Empty;
            this.LeftBorderColor = Color.Empty;
        }

        protected override void Paint(System.Drawing.Graphics graphics,
            System.Drawing.Rectangle clipBounds,
            System.Drawing.Rectangle cellBounds,
            int rowIndex,
            DataGridViewElementStates dataGridViewElementState,
            object value,
            object formattedValue,
            string errorText,
            DataGridViewCellStyle cellStyle,
            DataGridViewAdvancedBorderStyle advancedBorderStyle,
            DataGridViewPaintParts paintParts)
        {
            base.Paint(graphics, clipBounds, cellBounds, rowIndex, dataGridViewElementState, value, formattedValue, errorText, cellStyle, advancedBorderStyle, paintParts);
            //绘制边框颜色
            if (TopBorderColor != Color.Empty)
            {
                graphics.DrawLine(new Pen(TopBorderColor), cellBounds.X, cellBounds.Y, cellBounds.X + cellBounds.Width, cellBounds.Y);
            }
            if (RightBorderColor != Color.Empty)
            {
                graphics.DrawLine(new Pen(RightBorderColor), cellBounds.X + cellBounds.Width-1, cellBounds.Y, cellBounds.X + cellBounds.Width-1, cellBounds.Y + cellBounds.Height);
            }
            if (BottomBorderColor != Color.Empty)
            {
                graphics.DrawLine(new Pen(BottomBorderColor), cellBounds.X, cellBounds.Y + cellBounds.Height-1, cellBounds.X + cellBounds.Width, cellBounds.Y + cellBounds.Height-1);
            }
            if (LeftBorderColor != Color.Empty)
            {
                graphics.DrawLine(new Pen(LeftBorderColor), cellBounds.X, cellBounds.Y, cellBounds.X, cellBounds.Y + cellBounds.Height);
            }
        }
    }

使用方法：
DataGridViewColorColumnHeaderCell hc = new DataGridViewColorColumnHeaderCell();
hc.Value = "数值";//表头文本
hc.TopBorderColor = Color.Red;
hc.LeftBorderColor = Color.Red;
hc.RightBorderColor = Color.Red;
dataGridView1.Columns[1].HeaderCell = hc;