Gidday folks, I'm new here and I'm from Australia. The white markings on our aitcraft during WWII were for identification purposes as at the time most of the radial engined aircraft were of Japanese origin and a few Australian operated aircraft were shot down or shot at by Americans. Specifically Boomerangs, Catalinas and Vengeances. One famous American ace is actually photographed next to his P-38 and has an Austtralian flag on his scoreboard for sucessfully shooting down a Boomerang, (but not killing the pilot).
Some years ago I talked to a number of members of 24 Squadron who operated the Vengeance, and they said that their very first operation with the aicraft was rushed to the extent that radios had not been fitted, and some did not even have squadron codes. As they flew towards Moresby they were fired upon by the navy and had to take quick evasive action. They were then grounded until white markings were painted on to their machines.
Some of their stories were almost unbelievable, such as the pilot who got into a diving contest with a P-38 and ended up having to put both feet on the instrument panel to gain the leverage to pull out, and also ruptured his eardrums. Another occurance that was quite common in 24 Squardon was to end up with shrapnel from your own bomb in the tail of your aircraft.