That would be awesome if you could Customize the Background just like I can do in the original Messaging app on my Note 4.
If this happens then this app will definitely be 5 stars and over. Also to be able to send any type of file and any size. That will put this app Over The Top of all the other messaging apps out there on the Google Play Store. So Please fulfill this request. I already recommended this app to 5 people. Love this app.