The male of either of these two birds has an orange breast and the female has green mostly.
The difference between Orange-breasted Green-Pigeon and Pink-necked Green-Pigeon in Vietnam:
1/ Orange-breasted Green-Pigeon
Male: green neck;
Both sexes have a bluish nape.
2/ Pink-necked Green-Pigeon
Male: pink neck;
Female: green mostly.
