You could go with Diamond tetras. They're a sort of iridescent silver that might nicely offset all of the reds in the neons. Lemon tetras are pretty low key, but well fed under subdued lighting with a dark background and substrate and live plants (best display for tetras in general) they can really live up to the name. Ditto Flame Tetras (Von Rios).
What else? Pencilfish might be cool if you have a good lid. They're a more top strata fish, have the same sort of low bioload impact as neons, and have a unique rest position (sort of the opposite of a headstander), that can be a nice effect. They do jump, though.
Logic is only the beginning of wisdom