You may want to consider praecox rainbowfish aka dwarf neon rainbowfish. They max out at around 2 or 3 inches, are very nicely colored, and school. They also don't tend to bother many other fish. There is a picture of mine in my signature but it doesn't show their colors very well. Think along the lines of the blue in the german ram pictured next to them and imagine that color over the entire body with the exception of the fins which are either red or yellowish in color depending on the sex of the fish.