Pretty, peaceful, small but not tiny, schooling and not nippy, inexpensive and available, the Lemon Tetra, Hyphessobrycon pulchripinnis, has a lot going for it. Most of the time when you see these “fresh” they’re rather washed out; good care, good color diet feeding and patience can really reward you with spectacular displays. Mature males are really a sight to behold. Note, the wrong setting can make them feel uncomfortable, causing them to wash out. Heavily planted tanks, dark substrates, or tannin stained water, seem to really help them look their best. Most references suggest this species is native to the lower Rio Tapajos in Brazil, although there is some debate.
The Lemon Tetras I offer have been well-conditioned; when they got here they were simply gray and washed out, but now as they mature, the color is coming in. I took care of the boring part, now they’re ready to light up your aquarium! They do best in schools.
For those who are interested, check out this interesting documentation of Lemon Tetra aquaculture from the Center for Tropical and Subtropical Aquaculture. Some additional basic info can be found at the Microcosm Aquarium Explorer.