Color Testing...

Each square represents a cross-section of the Lab color space with a different lightness value (from 5 to 100). The a and b values vary along the x and y dimensions, respectively (from -100 to 100).

These ranges capture most of the L, a, b combinations that map to valid RGB values (between 0 and 255).

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.square {
  position:absolute;
  border: 1px solid gray;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
var lightness = d3.range(5, 101, 5),
    cols = 5,
    rows = Math.ceil(lightness.length / cols),
    margin = 10,
    side = (960 - margin) / cols - margin;

var x = d3.scale.linear()
  .domain([0, cols-1])
  .range([margin, margin + (side + margin) * (cols - 1)]);

var y = d3.scale.linear()
  .domain([0, rows-1])
  .range([margin, margin + (side + margin) * (rows - 1)]);

var ab = d3.scale.linear()
  .domain([0, side])
  .range([-100, 100]);

square.append('canvas')
    .attr('width', side)
    .attr('height', side)
    .style('width', side + 'px')
    .style('height', side + 'px')
    .each(render);

function valid(c) {
  return (c.r >= 0 && c.r <= 255 &&
          c.g >= 0 && c.g <= 255 &&
          c.b >= 0 && c.b <= 255);
}

function render(d) {
  console.log(d);
  var context = this.getContext('2d'),
      image = context.createImageData(side, side),
      i, j, c,
      idx = 0;

for (i = 0; i < side; i++) {
    for (j = 0; j < side; j++) {
      c = d3.lab(d, ab(j), -ab(i)).rgb();
      if (valid(c)) {
        image.data[idx++] = c.r;
        image.data[idx++] = c.g;
        image.data[idx++] = c.b;
        image.data[idx++] = 255;
      } else {
        image.data[idx++] = 120;
        image.data[idx++] = 120;
        image.data[idx++] = 120;
        image.data[idx++] = 255;
      }
    }
  }
  context.putImageData(image, 0, 0);
}

d3.select(self.frameElement).style("height", (rows * (side + margin) + margin) + "px");

</script>
</body>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js