In the test below the selected list item should appear together with a green marker. It works well for the initially selected item. However, it looks like #updateItem() isn't called when another item is selected which seems to be the reason of why the marker isn't updated properly.

see also http://stackoverflow.com/questions/34316254/javafx-rendering-selected-combobox-list-item

public class ComboBoxCellFactoryTest extends Application
{
  public static void main(String[] args)
  {
    Application.launch(args);
  }

  @Override
  public void start(Stage stage)
  {
    Parent content = createContent();
    Scene scene = new Scene(content, 400, 300);
    stage.setScene(scene);
    stage.show();
  }

  public Parent createContent()
  {
    FlowPane content = new FlowPane(10, 10);

    ComboBox<String> combo = new ComboBox<String>();
    combo.setItems(FXCollections.observableArrayList("Item 1", "Item 2", "Item 3", "Item 4"));
    combo.getSelectionModel().selectLast();
    combo.setCellFactory(new Callback<ListView<String>, ListCell<String>>()
    {
      @Override
      public ListCell<String> call(ListView<String> p)
      {
        return new ListCell<String>()
        {
          private final Rectangle rectangle;
          {
            rectangle = new Rectangle(10, 10);
          }

          @Override
          protected void updateItem(String item, boolean empty)
          {
            super.updateItem(item, empty);

            if (empty || item == null)
            {
              setText(null);
              setGraphic(null);
            }
            else
            {
              boolean selected = combo.getValue().equals(item);
              rectangle.setFill(selected ? Color.GREENYELLOW : Color.RED);
              setGraphic(rectangle);
              setText(item);
            }
          }
        };
      }
    });
    content.getChildren().add(combo);
    return content;
  }
}