Rainbowfish are the my favorite freshwater fish. I have a couple red's in one of my aquariums. One is a goldish hue and the other is a vibrant red. I've seen pale orange, brown, and even silver individuals aswell. Females are duller. They appreciate green in their diet. Kelp, spirilina.
Red rainbows are my favorite! They look just like little salmon. I have four adult males and they are all bright red with a day glow orange stripe from the face over to the tail in the morning when the brightest lights are on and I feed them. They love bloodworms and brineshrimp and I think this helps their color, I also have a lot of plants they snack on-- they especially like the roots of the amazon frog bit. An interesting thing happens in the afternoon and generally in the summer when my tank is much warmer: there will be a top/dominant male who is vibrantly colored but the others will be mostly silver. The dominant male switches off and they all seem to change color by the second during feedings or when they chase each other. Very fun and charming fish-- they always want to see what I'm up to and gather in a shoal to get close to where I am working on the tank.