If you look at pairs of notatus you'll see that the female is almost always solid green. My F1 had small spots until about 3" and then the green covered over them. Just pick one with a solid face. If it has any spots on its cheek at all, I'd automatically assume male.
Those fish are only 3.5 to 4 inches at the moment, either way I'm picking up my heroina and temensis tonight and I'm grabbing whatever female at the shop w/ no spots. He should already be holding her for me.