Rainbow Luminance by mbostock

The HSL rainbow (all hues at 100% saturation and 50% lightness) has highly variable luminance: we perceive some parts of the rainbow, such as between yellow and cyan, as significantly brighter than other parts of the rainbow. This, along with a lack of perceptual uniformity, makes the rainbow color scale unsuitable for visualization. Use the Lab or HCL color space instead.

index.html

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

body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
}

.space {
  position: absolute;
}

.space div {
  position: absolute;
  top: 0;
  left: 20px;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var spaces = [
  {
    name: "Rainbow (HSL)",
    color: function(t) {
      return d3.hsl(t * 360, 1, .5);
    }
  },
  {
    name: "Luminance",
    color: function(t) {
      var c = d3.hcl(d3.hsl(t * 360, 1, .5));
      c.c = 0;
      return c;
    }
  }
];

var y = d3.scale.ordinal()
    .domain(spaces.map(function(d) { return d.name; }))
    .rangeRoundBands([0, 500], .1);

var margin = y.range()[0],
    width = 960 - margin - margin,
    height = y.rangeBand();

var space = d3.select("body").selectAll(".space")
    .data(spaces)
  .enter().append("div")
    .attr("class", "space")
    .style("width", width + "px")
    .style("height", height + "px")
    .style("left", margin + "px")
    .style("top", function(d) { return y(d.name) + "px"; });

var canvas = space.append("canvas")
    .attr("width", width)
    .attr("height", 1)
    .style("width", width + "px")
    .style("height", height + "px")
    .each(function(d) {
      var context = this.getContext("2d"),
          image = context.createImageData(width, 1);
      for (var i = 0, j = -1, c; i < width; ++i) {
        c = d3.rgb(d.color(i / width));
        image.data[++j] = c.r;
        image.data[++j] = c.g;
        image.data[++j] = c.b;
        image.data[++j] = 255;
      }
      context.putImageData(image, 0, 0);
    });

space.append("div")
    .style("line-height", height + "px")
    .text(function(d) { return d.name; });

</script>