There are also physical differences as well, though they are hard to see by the inexperienced eye. I don't even know all of them yet, but I do know that the rostral process (the small crests on the snout) on the males is Usually larger or more pronounced in ambanjas. Some look like they have small horns! Ambanjas usually have a duller/less vibrant background with brighter bars. However people have been breeding them to get brighter colors all around and some have even been imported with vibrant backgrounds and equally vibrant bars. Personally I like the duller more layed back background with brighter bars look, especially when the background color is mostly powder blue or a pale yellow color.
EDIT: a yellow cheek is also sort of a 'trademark' of the ambanja, but not all of them have it and some other locales often have it.