New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  queryParams: ['color'],
  color: 'red'
});

application.template.hbs

<h2>Application-wide</h2>

<p>
  color: {{color}}
  {{link-to 'green' (query-params color="green")}}
  {{link-to 'blue' (query-params color="blue")}}
  {{link-to 'yellow' (query-params color="yellow")}}
</p>

{{outlet}}

index.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  applicationController: Ember.inject.controller('application'),
  color: Ember.computed.reads('applicationController.color')
});

index.template.hbs

<h2>Child one</h2>

<p>
  color: {{color}}
  {{link-to 'shirt' (query-params color=color)}}
  {{link-to 'pants' (query-params color=color)}}
  {{link-to 'shoes' (query-params color=color)}}
</p>

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}