Hi Alex T⚜️ 

Thank you for your reply, Hope this explanation helps. 

Please see the image at the end of this post. Primary Changes the Top and Bottom navigation bars, but it does not change the "android:navigationBarColor" which sits below the bottom navigation bar and it is not defined in the app theme. 

Adding "navigationBarColor:" line to Theme.js does not change the "navigationBarColor:" as it is not defined in the App. 

Please add this <item name="android:navigationBarColor">#e60000</item> to styles.xml in the Android folder and compile the app to see the bar in RED. 

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.DayNight.NoActionBar">
<!-- Customize your theme here. -->
<item name="android:textColor">#ffffff</item>
<item name="android:navigationBarColor">#e60000</item>
</style>