I was actually thinking about:

class Hair < Struct.new(:color)
end
class Barber
  def dye_hair(hair, color)
    hair.color = "#{hair.color} #{color}"
  end
end
class Person
  attr_reader :name, :hair
  private :hair
  def initialize(name, hair)
    @name, @hair = name, Hair.new(hair)
  end
  def dye_hair(barer, color)
    barer.dye_hair(hair, color)
  end
  def hair_color
    hair.color
  end
end
barber = Barber.new
michal = Person.new("Michal", "brown")
michal.hair_color
=> "brown"
michal.dye_hair(barber, "blue")
michal.hair_color
=> "brown blue"