That doesn't mean much...I was growing out my haitiensis fry and had one that was growing faster than everyone else, so I decided that it was a male and sold the rest and a few months later I found out that he was a she.
Females usually have black in the dorsal fin. It sometimes hard to tell, but at 6" I would say that if it doesn't have black, it's most likely a male. Good luck on pairing them.
Here's a couple pics of my pair. The female is on the left on both pics.