How to reference a theme attribute in a style?

I've got a following problem. I want to customize appearance of row in a list, but exception is thrown during inflating.

piece of code in style.xml

<style name="AppTheme.Main">     
    <item name="item_shadowColor">#000000</item>        
</style>
<style name="item_label">    
    <item name="android:shadowColor">?attr/item_shadowColor</item>        
</style>

attr.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="item_shadowColor" format="color" />
</resources>

list_item.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="wrap_content"
    android:orientation="horizontal" >

    <TextView
        android:id="@id/title"
        style="@style/item_label"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"/>

</LinearLayout>

And the exception

FATAL EXCEPTION: main
 android.view.InflateException: Binary XML file line #7: Error inflating class <unknown>
    at android.view.LayoutInflater.createView(LayoutInflater.java:606)
    at com.android.internal.policy.impl.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:56)
    at android.view.LayoutInflater.onCreateView(LayoutInflater.java:653)
    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:678)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:739)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
    at ru.mts.goodok.adapter.CategoryListAdapter.getView(CategoryListAdapter.java:30)
    at android.widget.AbsListView.obtainView(AbsListView.java:2052)
    at android.widget.ListView.mak