pulltorefresh修改背景

https://github.com/chrisbanes/Android-PullToRefresh/blob/master/sample/res/layout/activity_ptr_expandable_list.xml

<?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:orientation="vertical" >

    <!-- The PullToRefreshExpandableListView replaces a standard ExpandableListView widget. -->

    <com.handmark.pulltorefresh.library.PullToRefreshExpandableListView
        xmlns:ptr="http://schemas.android.com/apk/res-auto"
        android:id="@+id/pull_refresh_expandable_list"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        ptr:ptrHeaderBackground="@android:color/darker_gray"
        ptr:ptrHeaderTextColor="@android:color/white"
        ptr:ptrMode="pullUpFromBottom" />

</LinearLayout>