color function hcl inperpolation

hcl-interpolation.ts

  private getColor(i) {
    const color0 = '#00ca79';
    const color2 = '#7a4da8';

    const colorScale = d3
      .scaleLinear()
      .domain([0, categories.length - 1])
      .range([color0, color2])
      .interpolate(d3.interpolateHcl);

    return colorScale(i);
  }