title: Changing Spinner background generates dark colored border
body: <p>Using a simple spinner. When I scroll the spinner <strong>the shadow</strong> around spinner dropdown starts <strong>growing darker in color</strong>.</p>
  
  <p>I managed to fix the issue but</p>
  
  <blockquote>
    <p>I will appreciate if someone could explain me why was this
    happening?</p>
  </blockquote>
  
  <pre><code>&lt;Spinner
              android:id="@id/drop_list_1"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:layout_alignParentLeft="true"
              android:layout_alignParentStart="true"
              android:background="@android:color/transparent"
              android:dropDownSelector="@android:drawable/list_selector_background"
              android:dropDownWidth="wrap_content"
              android:minHeight="@dimen/min_header_height"
              android:popupBackground="#FFFFFF" /&gt;
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/DMbkV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DMbkV.png" alt="The dropdown list of spinner"></a></p>