code: function (color1, color2, weight) {
          if (!weight) {
              weight = new(tree.Dimension)(50);
          }
          var p = weight.value / 100.0;
          var w = p * 2 - 1;
          var a = color1.toHSL().a - color2.toHSL().a;
  
          var w1 = (((w * a == -1) ? w : (w + a) / (1 + w * a)) + 1) / 2.0;
          var w2 = 1 - w1;
  
          var rgb = [color1.rgb[0] * w1 + color2.rgb[0] * w2,
                     color1.rgb[1] * w1 + color2.rgb[1] * w2,
                     color1.rgb[2] * w1 + color2.rgb[2] * w2];
  
          var alpha = color1.alpha * p + color2.alpha * (1 - p);
  
          return new(tree.Color)(rgb, alpha);
      }
docs: Copyright (c) 2006-2009 Hampton Catlin, Nathan Weizenbaum, and Chris Eppstein http://sass-lang.com