docs: function() {
          var r = this.rgba[0] / 255, g = this.rgba[1] / 255, b = this.rgba[2] / 255;
          r = (r <= 0.03928) ? r / 12.92 : Math.pow(((r + 0.055) / 1.055), 2.4);
          g = (g <= 0.03928) ? g / 12.92 : Math.pow(((g + 0.055) / 1.055), 2.4);
          b = (b <= 0.03928) ? b / 12.92 : Math.pow(((b + 0.055) / 1.055), 2.4);
          return 0.2126 * r + 0.7152 * g + 0.0722 * b;
      }