k-9/res/drawable/message_list_item_background.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_window_focused="false" android:state_selected="true"
        android:drawable="@android:color/transparent"
        />
    <item android:state_selected="true"
        android:drawable="@android:color/transparent" />
    <item android:state_pressed="true" android:state_selected="false"
        android:drawable="@android:color/transparent" />
    <item android:state_selected="false"
        android:drawable="@android:color/transparent"
        />
</selector>