androidのSpinnerのDropDownListの背景を透過にする

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@drawable/backimage"
    android:orientation="vertical" >

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8" ?>
<shape  xmlns:android="http://schemas.android.com/apk/res/android"
android:shape ="rectangle">
<corners android:radius="5dip" />
<solid android:color="#AAFFFFFF"/> 
<padding
android:top="10dip"
android:bottom="10dip"
android:left="10dip"
android:right="10dip" />
<stroke
android:width="2dip"
android:color="#CCCCCC" />
</shape>

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:tileMode="repeat"
    android:src="@drawable/ic_launcher" />

package spinner.test.namespace;

import android.app.Activity;
import android.content.Context;
import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;

public class SpinnerTestActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        String[] s_items = {"RED", "BLUE", "BLACK", "YELLOW", "GREEN"};
        //普通のSpinner
        Spinner spinner1 = (Spinner)findViewById(R.id.spinner1);
        ArrayAdapter<String> adapter1 =
    		new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, s_items);
        adapter1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner1.setAdapter(adapter1);
        //カスタマイズSpinner
        Spinner spinner2 = (Spinner)findViewById(R.id.spinner2);
        //spinner2.setBackgroundColor(Color.parseColor("#AAFFFFFF"));//スピナーの背景色を指定
        spinner2.setBackgroundDrawable(getResources().getDrawable(R.drawable.list_border));//スピナーの背景画像を指定
        IntentItemArrayAdapter adapter2 =
        	new IntentItemArrayAdapter(this, android.R.layout.simple_spinner_item, s_items);
        adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner2.setAdapter(adapter2);
    }

    private class IntentItemArrayAdapter extends ArrayAdapter<String> {
        private int resourceId;
        private int resourceId2;
        public IntentItemArrayAdapter(Context context, int resourceId, String[] items) {
            super(context, resourceId,items);
            this.resourceId = resourceId;
            this.resourceId2 = resourceId;
        }
        public void setDropDownViewResource(int resourceId2){
            this.resourceId2 = resourceId2;
        }
        @Override
        public View getDropDownView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                LayoutInflater inflater = (LayoutInflater) getContext()
                        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = inflater.inflate(resourceId2, null);
            }
            TextView tv = (TextView) convertView.findViewById(android.R.id.text1);
            String cs=this.getItem(position);
            tv.setText(cs);
            tv.setTextColor(Color.parseColor(cs));//ここでリストの文字色を指定
            //((View) parent.getParent()).setBackgroundColor(Color.parseColor("#AAFFFFFF"));//リストの背景色を指定
            ((View) parent.getParent()).setBackgroundDrawable(getResources().getDrawable(R.drawable.list_border));//リストの背景画像を指定
            return convertView;
        }
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                LayoutInflater inflater = (LayoutInflater) getContext()
                        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = inflater.inflate(resourceId, null);
            }
            TextView tv = (TextView) convertView.findViewById(android.R.id.text1);
            String cs=this.getItem(position);
            tv.setText(cs);
            tv.setTextColor(Color.parseColor(cs));//ここでスピナの文字色を指定
              return convertView;
        }
    }


}