code: function(value) {
        var fillColor = value ? new fabric.Color(value) : '';
        if (!fillColor || !fillColor.getSource() || fillColor.getAlpha() === 1) {
          return 'fill="' + value + '"';
        }
        return 'opacity="' + fillColor.getAlpha() + '" fill="' + fillColor.setAlpha(1).toRgb() + '"';
      }
docs: Adobe Illustrator (at least CS5) is unable to render rgba()-based fill values we work around it by "moving" alpha channel into opacity attribute and setting fill's alpha to 1