Another option would to do something like that which is done for usplash, which Recommends: usplash-theme-ubuntu | usplash-theme (where usplash-theme is a virtual package that can be provided by any complaint usplash-theme)
Another option would to do something like that which is done for usplash, which Recommends: usplash- theme-ubuntu | usplash-theme (where usplash-theme is a virtual package that can be provided by any complaint usplash-theme)