Cant Have Custom Livery Trains In Formation Designer

the biggest drawback for me is that i cant put my liveries in custom formations

 

But you CAN use some of your own liveries in custom formations? (see below.......3 of my Sentinels coupled together).

However I do know that you can't do this for all vehicles..........in the same way that not all vehicles appear in free roam or Livery Designer.

What is it you are trying to use in FD that prompted this post?

 

multiple units