background transparency in TabWidget(android)

Sorry for my english. I cant do transparency in TabWidget. I use this:

0% (transparent) -> #00 in hex 20% -> #33 50% -> #80 75% -> #C0 100% (opaque) -> #FF

but change only shade color TabWidget. Its my xml:

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TabHost
        android:id="@android:id/tabhost"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:orientation="vertical" 

            >

            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="fill_parent"
                android:layout_height="0dip"
                android:layout_weight="1" 
                />

            <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:layout_weight="0"
                android:alpha="20"
                android:background="#D9214075" />

        </LinearLayout>
    </TabHost>



</RelativeLayout>