I guess under optimal lighting the finage has a reddish color along with the mother-of-pearl color from the body makes this vieja stands out from the Regani.
You have to see an adult argentea in person to realize how amazing they are. Argentea is easily one of the best looking cichlids out there, without a spec of color too.
Both fish are stunning, but i'm more partial towards V. regani at the moment. Here's some older photo's of my V. argentea, the fish is around 13" now, not quite as large as the fish in the photo but it is a tank raised specimen. I've also got V.regani, but these are still growing on.