Nah, I don't think so. I think the Golds are just more popular right now. To me Green Severums are just as beautiful as Golds.
The only sign of Severum aggression I've seen is with a pair that was given to the store I worked at. They were both torn up, mostly the female, their keeper said the male would do this to the female if he did not separate them right after spawning.....I've never heard of this happening other then this one time, maybe some one can shed some light on this...
But yeah, a 75g would be nice for a few Severums...