He means the red marble would be the more valuable. The long fins are pretty common now sadly (IMO breeding shouldn't be encouraged as they're badly deformed). I've personally never been lucky enough to see red marbles for sale locally or online, but I dont get out much so may be missing something there lol.
Edit - ug, just noticed both species you listed are long fins. Ignore my long fin comment, it's just my opinion. I think they're much prettier with the standard fins, and can swim better without them and therefore have a fuller life. Like I said though, just my opinion.