The leucs will be based mostly on body shape. Females will be kind of pear shaped between the front and hind legs, males will have almost straight sides...this is assuming the frogs are not overweight (like most of mine are!). The toepads on leucs tend to not differ much and the posture (sometimes an indicator in darts) doesn't either. How old are they? I have noticed that leucs take a little longer than tincs to mature (at least at my house they do).
I will try to take some comparison pictures tonight of a known pair to give you a good visual of the body shape.
I don't have any adult azureus right now but have a couple pairs of other tinc morphs. I will also try to get some good pictures of them for comparison that will apply to the azureus (like Eric said, the toepads are the key with them).