This can be a very attractive combination, but only if you have Black Faced birds with very good black markings. In many cases, the Chestnut Flanked White (CFW) mutation limits or dilutes the black on the belly.
Black Face Chestnut Flanked White male (in front) and Chestnut Flanked White male.
Chestnut Flanked White
Chestnut Flanked White (CFW for short) causes the body colour of the bird to lose or almost lose colour.
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.