title: d3.js scale-chromatic is not Working as Expected
body: <p>I have json data:</p>
  
  <pre><code>{
    "nodes": 
    [{"id": "Michael Scott"}, 
     {"id": "Jim Halpert"}, 
     {"id": "Pam Beasley"}
    ], 
    "links": 
    [{"source": "Michael Scott", "target": "Jim Halpert", "value": 50}, 
     {"source": "Michael Scott", "target": "Pam Beasley", "value": 25}
    ]
  }
  </code></pre>
  
  <p>I have code:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;meta charset="utf-8"&gt;
  &lt;style&gt;
  
  .links line {
    stroke: #aaa;
  }
  
  .nodes circle {
    pointer-events: all;
    stroke: none;
    stroke-width: 40px;
  }
  
  &lt;/style&gt;
  &lt;svg width="960" height="600"&gt;&lt;/svg&gt;
  &lt;script src="https://d3js.org/d3.v4.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://d3js.org/d3-scale-chromatic.v1.min.js"&gt;&lt;/script&gt;
  &lt;script&gt;
  
  var svg = d3.select("svg"),
      width = +svg.attr("width"),
      height = +svg.attr("height");
  
  var simulation = d3.forceSimulation()
      .force("link", d3.forceLink().id(function(d) { return d.id; }))
      .force("charge", d3.forceManyBody())
      .force("center", d3.forceCenter(width / 2, height / 2));
  
  d3.json("data.json", function(error, graph) {
    if (error) throw error;
  
    var link = svg.append("g")
        .attr("class", "links")
        .selectAll("line")
        .data(graph.links)
        .enter().append("line");
  
    var color = d3.scaleSequential(d3.interpolateBlues);
  
    var node = svg.append("g")
        .attr("class", "nodes")
        .selectAll("circle")
        .data(graph.nodes)
        .enter().append("circle")
        .attr("r", 2.5)
        .style("fill", function(d) { return color(d.value); })
        .call(d3.drag()
            .on("start", dragstarted)
            .on("drag", dragged)
            .on("end", dragended));
  
    node.append("title")
        .text(function(d) { return d.id; });
  
    simulation
        .nodes(graph.nodes)
        .on("tick", ticked);
  
    simulation.force("link")
        .links(graph.links);
  
    function ticked() {
      link
          .attr("x1", function(d) { return d.source.x; })
          .attr("y1", function(d) { return d.source.y; })
          .attr("x2", function(d) { return d.target.x; })
          .attr("y2", function(d) { return d.target.y; });
  
      node
          .attr("cx", function(d) { return d.x; })
          .attr("cy", function(d) { return d.y; });
    }
  });
  
  function dragstarted(d) {
    if (!d3.event.active) simulation.alphaTarget(0.3).restart();
    d.fx = d.x;
    d.fy = d.y;
  }
  
  function dragged(d) {
    d.fx = d3.event.x;
    d.fy = d3.event.y;
  }
  
  function dragended(d) {
    if (!d3.event.active) simulation.alphaTarget(0);
    d.fx = null;
    d.fy = null;
  }
  
  &lt;/script&gt;
  </code></pre>
  
  <p>This results in a force-directed graph without the nodes colored. Why aren't the nodes colored by the <code>var color = d3.scaleSequential(d3.interpolateBlues);</code> line coupled with the <code>.style("fill", function(d) { return color(d.value); })</code> line? Is it because <code>value</code> is attached to the links and not to the nodes? If so, how would I alter the code to show a color scale for the links?</p>
  
  <p>Thank you for any insight you all may have!</p>