I'm thinking of adding some rainbowfish in my tank and they seem to be a really good size and have a variety of different colours, plus they are mid level and very active fish. Makes them easily noticeable from across the room. Also, if you have good lighting, some of these rainbowfish show different colours depending on the side from which the light hits them, so they'll change colour as they swim around the tank. I haven't done all the homework researching about these, but from what I've read it looks like a lot of people disregard these fish cause they don't have all the vibrant colours when they are young (and in the fish shop), however they get lots of colour once they reach adulthood.