in your drawable:
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:state_selected="true"> <!-- selected -->
<shape
android:shape="rectangle">
<solid
android:color="#444444"/>
</shape>
</item>
<item> <!-- not selected -->
<shape
android:shape="rectangle">
<solid
android:color="#888888"/>
</shape>
</item>
</selector>