ComboBox color customization?

[Kubrix]

cbMain.Items.Add(new ListItem("Red", Color.Red));
cbMain.Items.Add(new ListItem("Green", Color.Green));
cbMain.Items.Add(new ListItem("Blue", Color.Blue));
cbMain.Background =  new SolidBrush(Color.Gray);
cbMain.FocusedBackground = new SolidBrush(Color.Yellow);

Expected: Gray background color of list, Yellow background color under selected item

Observed: