alphabackground.xml

    <RelativeLayout
        android:id="@+id/postHeader"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:layout_alignParentTop="true"
        android:background="@drawable/post_header_background" >

post_header_background.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <solid android:color="#88241101" />

</shape>