<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@color/red" android:state_pressed="false"></item>
    <item android:drawable="@color/blue" android:state_pressed="true"></item>
</selector>

<resources>
    <color name="red">#990000</color>
    <color name="blue">#000099</color>
</resources

android:background="@drawable/button_selector" >
 

//第二種
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item>
        <color android:color="#0f0"/>
    </item>
</selector>