They are sexually dimorphic in several ways. The males have a dark beak and facial features and darker orange or red markings on the neck and front legs. The males have a concave plastron for ease in mounting females. Females have a much lighter beak and face with light orange or yellow spots and patches on the head and neck. Females are more flat or rounded on their plastrons.
Babies tend to be very dark at first and lighten up and flatten out as they age.
Their spots also seem to be pigmentation that occurs later as the neonates mature. All though accurate sexing while small is difficult, it is possible to arrange the sex ratio of the clutch. Turtle eggs are temperature specific in the sex of the offspring produced. My group currently consists of 1.1 adults and 0.1 yearling. I consider myself still quite the amateur turtle keeper.