Private Binding

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  service: Ember.inject.service('thing-service'),
  
  actions: {
    changeColor() {
      const color = this.get('service.color');
      const colors = ['red', 'blue'];

      const newColor = colors
      	.reject((v)=> { return color === v})
      	.get('firstObject');

      this.set('service.color', newColor);
    }
  }
});

application.template.hbs

<h1>Color: <code>{{service.color}}</code>	</h1>
<button {{action 'changeColor'}}>Change Color</button>

services.thing-service.js

import Ember from 'ember';

const state = Ember.Object.extend({
  color: 'blue'
});

export default Ember.Service.extend({
	init() {
    
    const serviceState = state.create();
    
    Ember.defineProperty(this, 'color', Ember.computed({
    	get() {
      	return serviceState.get('color');
      },
      set(k, value, previous) {
        serviceState.set('color', value);
        this.notifyPropertyChange('color');
      }
    }).volatile());
    
	}
});

twiddle.json

{
  "version": "0.4.10",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.9/ember.debug.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.9/ember-template-compiler.js"
  }
}