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 + "%)" :