Changing code doesn't change that android application (java)

I'm beginning in android (and java) development, and am building of an example from google's documentation about fragmented applications and when changing activity_collection_demo.xml which according to android studio's find feature the only place where "#33b5e5"is being used (which is the color that shows you what tab you are on) When changing the color to another hexadecimal color, nothing changes. I've already tried to restart the emu. Also commenting the android.support.v4.view.PagerTitleStrip out has no effect on the code either.

here is the content of activity_collection_demo.xml

<!--
  Copyright 2012 The Android Open Source Project

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://ift.tt/jtTJvY

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  -->

<android.support.v4.view.ViewPager xmlns:android="http://ift.tt/nIICcg"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent">

<!--
This title strip will display the currently visible page title, as well as the page
titles for adjacent pages.
-->
<android.support.v4.view.PagerTitleStrip android:id="@+id/pager_title_strip"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="top"
    android:background="#33b5e5"
    android:textColor="#fff"
    android:paddingTop="4dp"
    android:paddingBottom="4dp"/>

</android.support.v4.view.ViewPager>

I would be very grateful if somebody could help me!