Actually, the Indian trigger and Durgeon are the same. The Hawaiian black and the durgeon are of the same genus but different species.
The Indian Black (Melichthys indicus) is more brown in color. Its tail is the same as the Pink tail and the clown trigger. Fan like.
The Hawaiian Black (Melichthys Niger) is dark black with Blue streaks in it. From certian angels it looks blue. It has a tail similar to that of the Blueline trigger (half moon).