World Map in D3v4 with Auto Colors

Redo of https://bl.ocks.org/mbostock/4180634 in D3v4

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  background: #fcfcfa;
}

.stroke {
  fill: none;
  stroke: #000;
  stroke-width: 3px;
}

.fill {
  fill: #fff;
}

.graticule {
  fill: none;
  stroke: #777;
  stroke-width: .5px;
  stroke-opacity: .5;
}

.land {
  fill: #222;
}

.boundary {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

</style>
<body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/topojson.v2.min.js"></script>
<script src="https://d3js.org/d3-geo-projection.v1.min.js"></script>
<script>

var width = 960,
    height = 580;

var color = d3.scaleOrdinal(d3.schemeCategory10);

var projection = d3.geoKavrayskiy7()
    .scale(170)
    .translate([width / 2, height / 2])
    .precision(.1);

var path = d3.geoPath().projection(projection);
  
var graticule = d3.geoGraticule();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

svg.append("defs").append("path")
    .datum({type: "Sphere"})
    .attr("id", "sphere")
    .attr("d", path);

svg.append("use")
    .attr("class", "stroke")
    .attr("xlink:href", "#sphere");

svg.append("use")
    .attr("class", "fill")
    .attr("xlink:href", "#sphere");

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("d", path);

d3.json("https://gist.githubusercontent.com/mbostock/4090846/raw/d534aba169207548a8a3d670c9c2cc719ff05c47/world-50m.json", function(error, world) {
  if (error) throw error;

var countries = topojson.feature(world, world.objects.countries).features,
      neighbors = topojson.neighbors(world.objects.countries.geometries);

svg.selectAll(".country")
      .data(countries)
    .enter().insert("path", ".graticule")
      .attr("class", "country")
      .attr("d", path)
      .style("fill", function(d, i) { return color(d.color = d3.max(neighbors[i], function(n) { return countries[n].color; }) + 1 | 0); });

});

d3.select(self.frameElement).style("height", height + "px");

</script>

https://d3js.org/d3.v4.min.js

https://d3js.org/topojson.v2.min.js

https://d3js.org/d3-geo-projection.v1.min.js