Much detailed information is only available in English:
The Black Face mutation causes the belly and the area between tear mark and beak to be filled with black pigment. Ideally, the belly should be as black as on the picture, but in real life, it is often less black.
This is a dominant mutation.
In Europe the general goal is to get the black to go as far back towards the tail as possible.
In Australia there are two varieties: Black Faced, where the black should go from breastbar to between the legs; and Black Bodied, which is the same mutation, but where the black should go beak to tail.
The black parts should be as black as possible. However, on most birds, there is still room for improvement, especially when studying details as above. All birds seen here were bred by me.
Breeders of Black Faced, please participate in the survey.