def nearest_value_cie94(css_color, threshold_distance = 100)
      value = Value.new(css_color)
      result_points = @tree.nearest_range(value.coords, threshold_distance)
      colors_to_values = Hash[result_points.map { |ea| [ea.data.color, ea.data] }]
      best_match_color = value.color.closest_match(colors_to_values.keys)
      colors_to_values[best_match_color]
    end
def nearest_value_cie94(css_color, threshold_distance = 100)
      value = Value.new(css_color)
      result_points = @tree.nearest_range(value.coords, threshold_distance)
      colors_to_values = Hash[result_points.map { |ea| [ea.data.color, ea.data] }]
      best_match_color = value.color.closest_match(colors_to_values.keys)
      colors_to_values[best_match_color]
    end
This implements the CIE94 color difference algorithm.
 See http://en.wikipedia.org/wiki/Color_difference#CIE94
 threshold_distance defaults to 40. Perceptible differences are > 2.3