ring-android/app/src/main/res/drawable/call_button.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:state_enabled="true" android:state_pressed="true">
        <shape android:shape="oval">
            <solid android:color="@color/sfl_light_blue" />
        </shape>
    </item>
    <item>
        <shape android:shape="oval">
            <solid android:color="@color/color_primary_dark" />
        </shape>
    </item>

</selector>