Winform ComboBox独立绘制下拉选项的字体颜色

众所周知，cbo1.ForeColor会同时改变cbo1.Text和下拉选项字体颜色。

独立绘制下拉选项字体颜色，ForeColor 只对 cbo1.Text 颜色有效的办法，示例：

private void cb7_DrawItem(object sender, DrawItemEventArgs e)
{
    DrawCboItems(sender, e);
}

private void cb7_SelectedIndexChanged(object sender, EventArgs e)
{
    SetCboTextColor(sender);
}

private void SetCboTextColor(object sender)
{
    ComboBox cbx = sender as ComboBox;
    if (cbx.Text == "+")
        cbx.ForeColor = Color.Red;
    else
        cbx.ForeColor = Color.Black;
}

private void DrawCboItems(object sender, DrawItemEventArgs e)
{
    ComboBox cbo = sender as ComboBox;

    //初始化字体和背景色
    Pen fColor = new Pen(Color.Black);
    Pen bColor = new Pen(Color.White);

    switch (e.Index)
    {
　　　　 //下拉选项的索引
    　　case 1:
    　　{
        　　fColor = new Pen(Color.Red);
        　　break;
    　　}
    }

    e.Graphics.FillRectangle(bColor.Brush, e.Bounds);
    e.Graphics.DrawString((string)cbo.Items[e.Index], this.Font, fColor.Brush, e.Bounds);
}