If you are looking for an active and colorful species to really add a splash of color to the tank but is peaceful with other fish, then look no further. Rainbows as a group are great fish: hardy, nonaggressive, and true to their name, very brightly colored.
Other species range through all the colors of the spectrum. Their one drawback is that they tend to be more expensive than your average smaller community tank fish, and usually run at least 10X's the price of common fish like livebearers. They are from Australian rivers, and some prefer water that is slightly on the hard side, though I haven't found this to be the case with neon rainbows (fine in neutral water, and can tolerate a broad range). They prefer meaty foods, and will quickly snatch it up when offered.
Rainbowfish must be given enough room to swim freely.