emptyColor (emptyColor) {
        if (!arguments.length) {
            return this._emptyColor;
        }
        this._emptyColor = emptyColor;
        return this;
    }
Set or get color for symbols when the group is empty. If null, just use the
{@link ColorMixin#colors colorMixin.colors} color scale zero value.
@param {String} [emptyColor=null]
@return {String}
@return {ScatterPlot}/