The person associated with AC/DC who most clearly illustrates the way that Australia was treated post-World War II is not a member of AC/DC but in fact their 1970s producer Harry Vanda. Vanda had previously been a member of the Easybeats, a popular 1960s band in Australia (which also featured George Young, the elder brother of Malcolm and Angus from AC/DC). The Youngs were recent immigrants from Scotland, and this was very much not out of the ordinary for members of Australian rock bands in the 1960s and 1970s - many of them had very recent British origins. Jimmy Barnes, the lead singer in Cold Chisel, the stereotypical Australian rock band in many ways, has a Scottish accent (as does Colin Hay of Men At Work, whose 'Down Under' apparently taught the world about vegemite sandwiches). Anyway, unlike all these Scots, Vanda was Dutch-born and his family immigrated to Australia post-war, as the Youngs did. The Easybeats - who in Australia are famous enough to merit a TV biopic - met in Villawood, the suburb of Sydney that had accommodation for recent immigrants (and which, up until after 1997, was the site of a centre which would house asylum seekers while their claims were assessed).

So why had the Dutch-born Harry Vanda emigrated to a British settler colony like Australia? Essentially, the history of the 20th century in Australia is the history of a slow, slow, transition between a British settler colony and being a nation of its own (the British monarch is still the titular head of state in Australia, mind you, so the transition is still incomplete). Post World War II, Australia had a desperate need for workers to do things like build the ambitious 'Snowy Mountains Scheme' - i.e., an ambitious hydroelectric dam in southern New South Wales (and clearly, World War II also scared Australia into wanting to be a bigger country, more capable of defending itself against aggressive northern neighbours - the slogan of the time was 'populate or perish').

The solution of the 1940s Labor immigration minister Arthur Calwell to these post-war problems was to start a scheme where people from Britain and Northern Europe were encouraged to migrate to Australia - this is the era of the '10 pound Pom' (i.e., the price of the fare to Australia on a boat was 10 pounds, and the British were 'Poms'). About a million British people indeed emigrate to Australia on this scheme after World War II (including the sister of The Kinks Ray Davies, an event he documents in the song 'Australia') - for many British people in the 1940s and 1950s, Australia would have seemed quite promising compared to the harshness and economic difficulties of post-war Britain (which still had World War II bombsites dotting the landscape in the 1960s).

However, post-war Northern European migration - which included Harry Vanda, from the Netherlands - dried to a trickle as the economies of Northern Europe began to recover from the war, and the scheme was expanded to include Southern Europeans; close to a million people from Southern Europe (Italy and Greece, largely) migrated to Australia between 1945 and 1975. It must be said the Australian immigration scheme during this period was famously run in a racist way, with immigrations officials famously having two versions of the English language test that they gave to prospective immigrants; they gave a much harder test to prospective immigrants who were not European in origin.

As to when Australia stopped being treated as a de facto British settler colony, there are a few dates you could use as endpoints. The most obvious one is 1901, when Australia became a federation and a country of its own, but Australian-born people were officially 'British subjects' rather than 'Australian citizens' until 1949, when due to legal changes people became eligible for Australian citizenship (something deemed necessary due to the immigration encouraged by Calwell). However, Australians also effectively retained British citizenship until 1984, and (as some recent Australians have found out, to their misfortune) they are still eligible for British citizenship if they have parents who were British subjects.

So you could probably argue that 1949 was the point where Australia literally stopped being a de facto British settler colony, and became, more broadly, a European settler colony. Similarly, over the 1960s and 1970s, various restrictions against non-European immigration were dismantled by the Menzies and Whitlam governments, and a large intake of refugees from South Vietnam were taken in by Australia; you could also argue that the dismantling of this 'White Australia policy' marks the point where Australia changed from a British settler colony that begrudgingly let in Europeans into a nation of its own. Perhaps the change of citizenship rules in 1984 marks that point, or the 1986 Australia Acts that removed any ability for the British parliament to make legislation about Australia. The point is that there was a slow trickle of changes over the 20th century whereby Australia slowly transitioned from colony to nation. Perhaps one could say that it's a long way to the top if you want to have a national identity of your own.