Find the color (out of an array of colors) that is most distant (brightness-wise) to the target color.

get_distant_brightness_color.js

var getDistantBrightnessColor = (function () {

  // Calculate grayscale color (luma) according to ITU-R Recommendation BT. 709
  var grayscaleLuma709Color = function(color) {
      return Math.round(0.2126 * color.r + 0.7152 * color.g + 0.0722 * color.b)
  };

  var linearDiffColor = function(color1, color2) {
      return Math.abs(color1.r - color2.r) +
          Math.abs(color1.g - color2.g) +
          Math.abs(color1.b - color2.b);
  };

  return function (color, matches) {
      var distances = [];

      // Prepare an array of colors with their distances from the target color
      for (var i = 0; i < choices.length; i++) {
          distances.push({
              color: matches[i],
              distance: 
                  Math.abs(grayscaleLuma709Color(matches[i]) - grayscaleLuma709Color(color)) +
                  linearDiffColor(matches[i], color)
          });
      }

      // Sort in reverse order, to get the best contrast first
      distances.sort(function(a, b) {
          return b.distance - a.distance
      });

      return distances[0].color
  };
});