toHslString: function() {
            var hsl = rgbToHsl(this._r, this._g, this._b);
            var h = mathRound(hsl.h * 360), s = mathRound(hsl.s * 100), l = mathRound(hsl.l * 100);
            return (this._a == 1) ?
              "hsl("  + h + ", " + s + "%, " + l + "%)" :