code: function(rgba, offset) {
          rgba = rgba || [];
          offset = offset || 0;
  		rgba[offset++] = this.rgb[0];
  		rgba[offset++] = this.rgb[1];
  		rgba[offset++] = this.rgb[2];
  		rgba[offset] = this._alpha;
  		return rgba;
  	}
docs: to an Array of RGBA values
  @param rgba
  @param offset (optional)
  @return rgba array