How to reference a color attribute in a style

I want to use same drawable (having different colors) as background for all the buttons in one layout.

drawable/my_vector.xml

<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://ift.tt/nIICcg"
    android:height="60px"
    android:width="360px"
    android:viewportHeight="60"
    android:viewportWidth="360" >

    <path
        android:name="bottom"
        android:pathData="M 0,60 L 360,60"
        android:strokeColor="?attr/testColor"
        android:strokeWidth="4" />

</vector>

Above code will draw a horizontal line having storke width = 4px if I directly substitute strokeColor value [android:strokeColor="#ffff0000"]

But as per requirement, background can have different colors. That is why I have added ?attr/testColor and want to define it using style.

values/attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:android="http://ift.tt/nIICcg">

    <declare-styleable name="dummyStyle">
        <attr name="testColor" format="color|reference" />
    </declare-styleable>

</resources>

values/styles.xml

<resources xmlns:android="http://ift.tt/nIICcg"
    <!-- Application theme. -->
    <style name="AppTheme" parent="AppBaseTheme">

        <!-- <item name="testColor">#ff0000ff</item> -->

    </style>

    <style name="MyButton" parent="android:Widget.DeviceDefault.Button">
        <item name="android:background">@drawable/my_vector</item>
    </style>

    <style name="MyButton.Green">
        <item name="testColor">#ff00ff00</item>
    </style>

    <style name="MyButton.Red">
        <item name="testColor">#ffff0000</item>
    </style>
</resources>

layout.xml

<LinearLayout xmlns:android="http://ift.tt/nIICcg" xmlns:tools="http://ift.tt/LrGmb4"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <Button
        android:layout_marginTop="10px"
        android:id="@+id/test01"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="@style/MyButton.Green"
        android:text="Test01" />

    <Button
        android:layout_marginTop="10px"
        android:id="@+id/test02"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="@style/MyButton.Red"
        android:text="Test02" />

</LinearLayout>

What works:
If I uncomment testColor in AppTheme, then all buttons have blue-color line as a background.

What does not work:
If I use 2 different styles having different colors (MyButton.Green, MyButton.Red) by applying it on Button, all I get is a transparent background.