Background

[Btxprss]

Ima float this idea out there

Background wallpaper in the messenger and text app 

[MarvinMod2]

There already is, open a message in the stock Samsung messaging app, click the 3 dots in top right corner, click customize chat room.

[Btxprss]

Ooh OK thanks friend

[USBetaModerator2]

Hello,
Thank you very much for your feedback.

We appreciate your contribution to the beta program.

Regards,
One UI Beta Team