Ared-eyed fly mates with a blue-eyed fly. the offspring all have red eyes. what is the dominant trait?

It is likely that the red eye trait is dominant if a red eye and blue eye fly have only red eyed offspring. However, it's doable that the blue round-eyed attribute is dominant and also the blue round-eyed fly has the red round-eyed citron and passed it on to its offspring on every occasion.