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:endColor="@color/colorPrimary"
        android:startColor="@color/colorAccent"
        android:type="linear" />
</shape>