help on has_one

I'm having:    colour model with id,name,value    car model, id,name,colour_id    chair model id,name,colour_id - i have a many to one relation, correct? - different type of objects have a colour. putting for the car and chair model an attribute has_one :colour, is't enough. I thought that having:

class Car<ActiveRecord::Base   has_one :colour   def before_create()     colour = Color.new     colour.name = 'red'     color.save   end end

when I would create a Car object and save-it i should have in the database for that record color_id <> 0, but i found that it is NULL. -what did I do wrong?