public ObjectProperty<Color> knobColorProperty() {
        if (null == knobColor) {
            knobColor  = new ObjectPropertyBase<Color>(_knobColor) {
                @Override protected void invalidated() { fireTileEvent(RESIZE_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "knobColor"; }
            };
            _knobColor = null;
        }
        return knobColor;
    }
Defines the color that will be used to colorize the knob of
the radial tiles.

@param COLOR
src/main/java/eu/hansolo/tilesfx/Tile.java