What are green oranges called?

The Green Orange (Cam Sanh) originated from Vietnam, it is a hybrid variety, possibly between the Mandarin Orange (Citrus reticulata) and the Pomelo (Citrus maxima), which has been cultivated since ancient times in Vietnam.

The fruit may be easily recognized by its thick skin, which is typically bright green (because of which, it is sometimes referred to as a green orange), although the skin may also be partly green and partly orange, or entirely orange. Its flesh is orange, dark and sweet.. 

Generally the Citrus fruit is called "orange" in the Western because of it has orange color when the fruit ripe. The Cam Sành in Vietnam is a special hybrid species of Citrus fruits that has green color of skin when it is ripe then it is planted in the South of Vietnam so it is called "green orange"