code: function rgb(red, green, blue){
    switch (arguments.length) {
      case 1:
        utils.assertColor(red);
        var color = red.rgba;
        return new nodes.RGBA(
            color.r
          , color.g
          , color.b
          , 1);
      default:
        return rgba(
            red
          , green
          , blue
          , new nodes.Unit(1));
    }
  }
docs: Return a `RGBA` from the r,g,b channels.
  
  Examples:
  
  rgb(255,204,0)
  // => #ffcc00
  
  rgb(#fff)
  // => #fff
  
  @param {Unit|RGBA|HSLA} red
  @param {Unit} green
  @param {Unit} blue
  @return {RGBA}
  @api public