ModifiedComboBox.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Drawing;

namespace ModifiedControls
{
    class ModifiedComboBox : ComboBox
    {
        new public System.Windows.Forms.DrawMode DrawMode { get; set; }
        public Color HighlightColor { get; set; }

        public ModifiedComboBox()
        {
            SetStyle(ControlStyles.Selectable, false);
            base.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;
            this.HighlightColor = Color.Gray;
            this.DrawItem += new DrawItemEventHandler(AdvancedComboBox_DrawItem);
        }

        void AdvancedComboBox_DrawItem(object sender, DrawItemEventArgs e)
        {
            if (e.Index < 0)
                return;

            ComboBox combo = sender as ComboBox;
            if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
            {
                e.Graphics.FillRectangle(new SolidBrush(HighlightColor), e.Bounds);
                e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font, new SolidBrush(combo.BackColor), new Point(e.Bounds.X, e.Bounds.Y));
            }
            else
            {
                e.Graphics.FillRectangle(new SolidBrush(combo.BackColor), e.Bounds);
                e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font, new SolidBrush(combo.ForeColor), new Point(e.Bounds.X, e.Bounds.Y));
            }
            e.DrawFocusRectangle();
        }
    }
}