TMR put this up on their Facebook asking who has to give way, but that's too easy. A much more complicated question is: what does the law say around indicating?
I've seen people say only blue must indicate, others say both must indicate, and yet others say neither must indicate. Which is correct?
Whoever is in front has right of way at these. It's unlike a situation where one lane ends (indicated by a dotted line that runs out), in which case the person in the continuing lane has right of way.
You could take a look at your state's laws to verify, but I strongly suspect the answer will be the same wherever in Australia you go. Our road rules are relatively standardised, even though it's all state legislation.
Of course whoever is in front has the right of way but sometimes you have smartarses coming up beside you to overtake. All I'm saying is let them go ahead. It's not worth your life to prove a point.