public ObjectProperty<TileColor> trackColorProperty() {
        if (null == trackColor) {
            trackColor = new ObjectPropertyBase<TileColor>(_trackColor) {
                @Override protected void invalidated() { fireTileEvent(REDRAW_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "trackColor"; }
            };
            _trackColor = null;
        }
        return trackColor;
    }
Defines an optional node that can be used in combination with the
CustomTileSkin.
@param GRAPHIC
src/main/java/eu/hansolo/tilesfx/Tile.java