Jim, wheel center caps are not a "one size fits all" proposition. Each wheel manufacturer makes caps to fit their wheels. Some snap in, some are held on with screws. Ask Rota for caps. I would be surprised if the Subaru caps fit, although it would look very "trick" if they do!
The caps came with my wheels(Rota Subzeros). I had to put them on. They are black, with a carbon fiber look alike finish on the side. It's ok. Not the best. I didn't like them at the beginning and now I really don't care at all. Wait until you get the wheels and shop around with one of the Rotas in your hand so you will make sure you get the right fit. Many people just don't put them on. I think it looks even worse. It's up to you and what you like.