Take a look at this thread, it explains it all, even how to use only one image with different effects. From it:
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_pressed="true" android:drawable="@drawable/rbutton_pressed" />
<item android:state_focused="true" android:drawable="@drawable/button_focus" />
<item android:drawable="@drawable/button_rest" />
</selector>
This is the method with three different drawables. With the following code you can appli some effects, as stated in the thread:
button.getBackground().setColorFilter(0xFF00FF00, PorterDuff.Mode.MULTIPLY);
or
button.getBackground().setColorFilter(new LightingColorFilter(0xFFFFFFFF, 0xFFAA0000));