code: function() {
        var source = this.getSource(),
            average = parseInt((source[0] * 0.3 + source[1] * 0.59 + source[2] * 0.11).toFixed(0), 10),
            currentAlpha = source[3];
        this.setSource([average, average, average, currentAlpha]);
        return this;
      }
docs: Transforms color to its grayscale representation
  @method toGrayscale
  @return {fabric.Color} thisArg