ordinalColors (r) {
        return this.colors(scaleOrdinal().range(r));
    }
Convenience method to set the color scale to
{@link https://github.com/d3/d3-scale/blob/master/README.md#ordinal-scales d3.scaleOrdinal} with
range `r`.
@memberof ColorMixin
@instance
@param {Array<String>} r
@returns {ColorMixin}