可以创建自定义颜色表并更改渲染器属性：

public class MenuColorTable : ProfessionalColorTable
{
    public MenuColorTable()
    {
        UseSystemColors = false;
    }
    public override Color MenuBorder
    {
        get { return Color.Fuchsia; }
    }
    public override Color MenuItemBorder
    {
        get { return Color.DarkViolet; }
    }
    public override Color MenuItemSelected
    {
        get { return Color.Cornsilk; }
    }
    public override Color MenuItemSelectedGradientBegin
    {
        get { return Color.LawnGreen; }
    }
    public override Color MenuItemSelectedGradientEnd
    {
        get { return Color.MediumSeaGreen; }
    }
    public override Color MenuStripGradientBegin
    {
        get { return Color.AliceBlue; }
    }
    public override Color MenuStripGradientEnd
    {
        get { return Color.DodgerBlue; }
    }
}

变更Renderer：

contextMenuStrip1.Renderer = new ToolStripProfessionalRenderer(new MenuColorTable());

结果如下：