Rainbowfish as the name suggests are very colourful attractive fish, unfortunately they do not look their best when for sale in an aquarium. Combination of stress caused by being moved around and being in a busy pet / aquatic shop with lots of people dulls their colours. Plus the ones shown in shops will be juveniles and not showing their full adult colours.
There are a wide range of different Rainbow Fish in existence but most species are hard to get hold of. The wide range of colours and body shapes makes it hard to believe they are from the same family of fish.
They mainly originate from Australia and New Guinea, but they have been discovered further afield.
Recently there has been a surge in popularity of these fish. They are peaceful creatures which do well in the community aquarium.
Their water chemistry preferences change considerable cross the different species, with some fish preferring very acidic water and others preferring very alkaline water. The similar differences apply to water hardness and temperature.