i was actually reading that they start to show sex about 2-3 in, and the male is more brilliantly colored; spangles and orange tail fringe.
only problem is i just bought what i thought was two male gts and then four days later; these r only 2 inches mind u; the most brilliantly colored and darkest one laid eggs. so i think the coloration and elongating of the fins and fringe is much more accurate after maybe 4-5 in.
"Sexing. Male green terrors grow larger and more colorful than females. They also grow the typical male cichlid nuchal (whatever that means) bump on their forehead as they mature. Two males in a small tank may will present a problem."