on my African tetra tank, I bought 3 of what ever was available, until the tank got crowded... most were juvenal, seems like on Africans, most just start out silver, then as they develop they get pretty... 1st to mature or at least get colorful, were the commonly available "Congo Tetra" Phenacogrammus interruptus... these are likely all farm raised now...& they could easily be a favorite, if I didn't go & buy so many others... the "Gold, Blue eye" Phenacogrammus aurantiacus was probably the most colorful from the start, & they are one of my favorites... the "Fantastics" Phenacogrammus sp. fantastique look pretty interesting, & I have some Blue Alestopetersius brichardi, that are just starting to color up & get their trident tails, I also bought a few red's, but they were quite a bit smaller, & haven't started to color up yet...
In general, South American Tetras, like the Cardinals, for example, seem to color up at a younger age, so you know what you are getting sooner... my school of Platinum Rummy Noses are one of my favorites, colorful, & active... getting them to live beyond a couple days in your tank might be challenging, but mine seem pretty stable after a week or so, & now mine are dancing pretty much every morning, at 1st light... I have about a Dozen...