The most colorful 55 suitable tangs that come to mind are cyprichromis, just stay away from the jumbos. I would recommend searching the species profiles section, as you can get a lot of ideas there, as well as get a better feel for what you want.
i second the his & her thing. if she wants color get her into fishkeeping.. worked on my gf. she read up on discus bought books and such.. and now has some amazing discus. its fun to watch her working on her own tank rathering then commenting on mine.. .