title: Why doesn't android:colorBackground work?
body: <p>In this HelloWorld app, I'm using the <code>android:colorBackground</code> property, but it doesn't apply the red background.</p>
  
  <p><strong>AndroidManifest.xml</strong>:</p>
  
  <pre><code>&lt;application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:supportsRtl="true"
      android:theme="@style/AppTheme" &gt;
      &lt;activity
          android:name=".EditTextActivity"
          android:label="@string/app_name" &gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.MAIN" /&gt;
  
              &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;
  &lt;/application&gt;
  </code></pre>
  
  <p><strong>Layout xml</strong>:</p>
  
  <pre><code>&lt;RelativeLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".EditTextActivity"&gt;
  
      &lt;TextView
          android:text="Hello World!"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:textSize="40sp"
          /&gt;
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p><strong>style.xml</strong>:</p>
  
  <pre><code>&lt;resources&gt;
      &lt;!-- Base application theme. --&gt;
      &lt;style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"&gt;
          &lt;item name="android:colorBackground"&gt;#ff0000&lt;/item&gt;
      &lt;/style&gt;
  &lt;/resources&gt;
  </code></pre>
  
  <p>The result looks like this (with no red color background):
  <a href="https://i.stack.imgur.com/Tb5Me.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Tb5Me.png" alt="Hello World "></a></p>