Neons and Black Neons are not the same genus, and are not really closely related. Shoaling is a defensive strategy adopted by fish when they feel threatened, it is rarely seen in small tanks. In big tanks with a lot of open space, both those species will stick to their own, and if really threatened may form a mixed school, but if they are that scared, then you have bigger issues.
Yeah, that's exactly what I read elsewhere, albeit that particular site didn't seem all that credible. As for shoaling, my Neons almost never stick together anyway!
The Black Neon never appealed to me much in pictures, but I saw them at my LFS recently - they are beautiful little fish. Same with the Silvertips. I think either of these would contrast nicely with a group of Neons.
The Black Neon is a seriously under rated fish IMHO. They are a lot hardier then Neons, and have an elegence about them which is to best appreciated in vivo.
when i had just tetras in my tank i used to get 10 neons 10 glow lights 2 cat fish and 3 black neons all school together when it was dark
it was really cool seeing them