A few months ago, Google revealed its app for a chat in order to compete with other chatting apps. Google has now updated its app with a lot of improvements that are needed a lot.
Obviously, WhatsApp users may have noticed that many of the chat themes are hidden or missing in the Allo. Some of the users have tried to enable hidden themes and which can be enabled on a per-user basis.
You may not be able to see the themes in the apps from the play store but you can enjoy numerous themes in the Allo APK. Still, users are expecting to make the update and allow users to use themes. Users may not be able to enable the themes in the main app which you downloaded from the play store.