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?