java/com/android/incallui/commontheme/res/color/incall_button_ripple.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:color="#80888888" android:state_checked="true"/>
  <item android:color="#80ffffff"/>
</selector>