Are you putting the female into the male's enclosure when you introduce? If so, you may want to consider neutral territory.
We have a 14 month old nosy female that was the same way. Each time we put her in with one of the males - she would become aggressive, turn dark and fend off the male. We didn't give up - every week we would try again. We even tried other males - at other breeder's locations - no luck.
Then one day, one of our ambanja pairs decided to breed while outside sunning (we have a bunch of 12ft maple trees). The male kept going down his tree and towards her tree! Finally, we took down the barrier and he went up her tree and mating commenced.
Since the male finds the female in the wild - why do we put the female into the male's cage..????? Not sure who decided it was the best approach. We have since done some experiments with this method, and find that neutral territory works great. Even if the neutral area is a branch on the floor!
Our nosy female finally consented - when the male came onto the tree she was sunning herself on. You might want to try this approach.
Morgana - Reptayls, Ltd.