Sevs are easy to sex once you know what to look for. the down side to it is they almost have to be full grown before they show sexual dimorphism's (sp?)
Males most often will have stripes on their face longer filaments on the dorsal and anal fin and the anal fin will turn bright red when in the mood for spawning.
Females show non of these traits, but green females do tend to become more boldly striped when in the mood for some sweet lovin.