public void setFillWithGradient(final boolean FILL_WITH_GRADIENT) {
        if (null == fillWithGradient) {
            _fillWithGradient = FILL_WITH_GRADIENT;
            fireTileEvent(REDRAW_EVENT);
        } else {
            if (!fillWithGradient.isBound()) {
                fillWithGradient.set(FILL_WITH_GRADIENT);
            }
        }
    }
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