Threema-Android-mirror/app/src/main/res/drawable/ic_launcher_background.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
	<gradient
		android:angle="90"
		android:startColor="#FF494949"
		android:endColor="#FF373737"
		android:type="linear"/>
</shape>