Create a stateful color for your button, just like you did for background, for example:
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<!-- Focused and not pressed -->
<item android:state_focused="true"
android:state_pressed="false"
android:color="#ffffff" />
<!-- Focused and pressed -->
<item android:state_focused="true"
android:state_pressed="true"
android:color="#000000" />
<!-- Unfocused and pressed -->
<item android:state_focused="false"
android:state_pressed="true"
android:color="#000000" />
<!-- Default color -->
<item android:color="#ffffff" />
</selector>
Place the xml in a file at res/drawable folder i.e. res/drawable/button_text_color.xml. Then just set the drawable as text color:
android:textColor="@drawable/button_text_color"