Are you feeding your pacu lots of veggies and fruit ..because mine kept the color red for many years.. they need a little protein too but more veggies and some fruit make them color up nice.
If you have $$1,000 then you can get a sheep pacu. They are not very known to the fish hobby, only people that have them are aquariums and if your lfs does get them , they will probably be around 500$-1,000$!