WhatsApp will soon allow you to set different wallpapers for different chats
The feature is under development and it will be only available in the future. However, if you are a beta user, you can update your WhatsApp on your Android device get a glimpse of the upcoming feature. Apart from this, WhatsApp will also let users add doodles to a standard plain wallpaper and reduce the opacity of the wallpaper. You can choose whether you want your wallpaper to be prominent or subtle. However, if you don't want to make any changes to the wallpaper, you can also let the plain wallpaper remain.