Android : View background color can not work with selector?

I am working on an android application , and I have a lot of items to display by the ListView:

    <ListView
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:id="@android:id/list"
            android:layout_gravity="right|center_vertical"
            android:listSelector="@drawable/bg_selector"/>  

bg_selector.xml:

<?xml version="1.0" encoding="utf-8"?>
<selector
        xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true" android:drawable="#8F136fb8"/>
</selector>

And I want each item have a different background color, and I set them in the getView method of the adapter:

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        .....
        Color color=generateColor();
        viewHolder.textView.setBackgroundColor(color);
        return convertView;
    }

However I found that that once I select an item, there is no effect responded to the user event I set the selector to the ListView