We have all seen the white square at the top type of a notification in the notification bar.
Well, it is pretty easy to fix it if you are using Firebase, but still, using a colored icon won’t fix it. You can try to add this metadata:
<meta-data android:name="com.google.firebase.messaging.default_notification_icon" android:resource="@mipmap/ic_launcher" />
and it will probably work on some devices. But to really fix it you need to make a specific white icon for it. Here is the LINK & LINK to the Google icon guidelines. Otherwise, your app will default to the white square icon. And HERE is the issue from StackOverflow. So better make a white icon and use it in the notification builder or in the AndroidManifest file or it will not show.