public BooleanProperty fillWithGradientProperty() {
        if (null == fillWithGradient) {
            fillWithGradient = new BooleanPropertyBase(_fillWithGradient) {
                @Override protected void invalidated() { fireTileEvent(REDRAW_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "fillWithGradient"; }
            };
        }
        return fillWithGradient;
    }
Defines the usage of a gradient defined by gradientStops to fill the area
in the SmoothAreaTileSkin
@param FILL_WITH_GRADIENT
src/main/java/eu/hansolo/tilesfx/Tile.java