A good compromise between the current flag, the Blue Ensign and a tabula rasa with just green and gold, with few links with the Blue Ensign would be Blue and Gold Auspale.
This is like the Green and Gold Auspale, but with blue instead. This flag is about one third in yellow with on the left top, a blue Commonwealth Star The two other thirds has got a blue frame with in the centre a yellow Southern Cross.
Blue is indeed the third de facto national colour and people are used to this colour To mix with one of the two national colours: yellow, the most suitable for a association with blue (as I think green and yellow make dull because they're rather close colours, there is not enough a contrast).
So why not?