observing sub-properties of ember data object

api_result.json

{
  "thing": "Thing",
  "colors": {
    "primary": "#000000",
    "secondary": "#FFFFFF"
  }
}

colors.js

import Ember from 'ember';
import DS from 'ember-data';

var defaultColors = {
  primary:   '#8e247b',
  secondary: '#5dd4fa'
};

export default DS.Transform.extend({
  deserialize: function(serialized) {
    if (Ember.isEmpty(serialized)) {
      return Ember.Object.create(defaultColors);
    }
    return Ember.Object.create(serialized);
  },

  serialize: function(deserialized) {
    return deserialized;
  }
});

thing.js

export default Model.extend({
  
  thing: attr(),
  // how can I dirty the model when colors.primary, colors.secondary changes?
  colors: attr('colors')
  
});

Observing nested properties this way is extremely problematic. You can keep pounding on this door, but you're going to have a bad time. You would be better off extracting properties from this nested object in the serializer with a goal to end up with

export default Model.extend({
  thing: attr(),
  // how can I dirty the model when colors.primary, colors.secondary changes?
  colorsPrimary: attr('string'),
  colorsSecondary: attr('string')
});