Ref: https://stackoverflow.com/questions/21231404/how-to-change-background-color-popup-menu-android/30731151
Add Popup-Menu style to your App-Theme:
<style name="AppTheme" parent="android:Theme.Light">
<item name="android:popupMenuStyle">@style/PopupMenu</item>
</style>
<style name="PopupMenu" parent="@android:style/Widget.PopupMenu">
<item name="android:popupBackground">@android:color/white</item>
</style>