Emperor tetra types

The other day I went to a pet store, wanting to buy some emperor tetras. They didn’t have the standard purple/blue ones, but they did have what was labeled “black emperor tetras”, the ones that look like this:
The employee told me she thought they were a different species than the purple ones, so I didn’t buy any. But now I’m curious, are they the same species but just a different morph? Or are they two separate species with the same name? They were definitely bigger than the purple ones I have. Could I mix them or should I wait till they have more purple emperors?
Yes they are different species. The fish pictured above is the emperor tetra - Nematobrycon palmeri. The purple emperor/royal tetra is Inpaichthys kerri. Different species, different genus. Wait for more of the purples if that is the species you want.

Purples are smaller and apparently they are better schoolers.
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Thanks! I didn’t think they looked similar enough to be the same species but you never know with fish.
So Black Emperors are just a color variant of regular Emperor Tetras. Just to avoid some confusion that I see here, let's show some pictures:

This is a male Emperor Tetra, Nematobrycon palmeri. Well known for many decades:
Nematobrycon palmeri.jpg

This is a Black Emperor Tetra. It is a color variant of the common Emperor Tetra, first produced around 1970, but suddenly became more popular just a few years ago:
Nematobrycon palmeri Black male02.JPG

And this fish is a different genus and species, which has gotten quite popular. It has several common names, including Purple Emperor, Blue Emperor, King Tetra, and Purple Neon. It is Inpaichthys kerri, and is actually not that closely related to the Nematobrycon genus:
Inpaichthys kerri male 01.jpg

And just for good measure, this last fish is known as the Red Eyed Emperor, also the Rainbow Emperor, Nematobrycon lacortei:
Nematobrycon lacortei male1.jpg

Any Questions?
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