Django adding `choices` to an inherited model field

Question

Using multi-table inheritance, I have two models:

class Bird(models.Model):
    color = models.CharField()

class Bluebird(Bird):
    ...

Using these models, I can do this:

birds = Bird.objects.all()
for bird in birds:
    print bird.color

This is super simple, but I don't like allowing people to define arbitrary color values in some cases. For example, I want to prevent users from creating Bluebird objects for which the color field is set to anything but "blue" or, in more rare cases, "grey" or "brown". In other words, I want to set the choices kwarg on the inherited color field from within the Bluebird model. From a cursory internet search, it seems that Django doesn't currently allow model subclasses to override the fields from a parent.

How does one retain access to the color field in the parent class while defining acceptable choices in the child?

EDIT: This question focuses on Django < 1.8. In 1.8, the ability to pass a callable for a field's choices kwarg was added, and while that would be nice, I'm dealing with a system that hasn't yet been upgraded and upgrading is not currently an option.

Answer 1

Use a property.

You can define the color value for each model and then return that as a property, if the color will be fixed, you don't need it in the database.

class Bird(models.Model):
   COLOR = None

   @property
   def color(self):
       return self.COLOR

class BlueBird(Bird):
   COLOR = 'Blue'

>>> b = BlueBird()
>>> b.color
'Blue'