code: function green(color, value){
    color = color.rgba;
    if (value) {
      return rgba(
        new nodes.Unit(color.r),
        value,
        new nodes.Unit(color.b),
        new nodes.Unit(color.a)
      );
    }
    return new nodes.Unit(color.g, '');
  }
docs: Return the green component of the given `color`,
  or set the green component to the optional second `value` argument.
  
  Examples:
  
  green(#0c0)
  // => 204
  
  green(#000, 255)
  // => #0f0
  
  @param {RGBA|HSLA} color
  @param {Unit} [value]
  @return {Unit|RGBA}
  @api public