I know there are other questions comparing the US and UK usage of o and ou in words like colour. My question is specifically in regard to Australian English. I was always taught that here in Australia we use ou and that the other variant was yet another example of the insidious corruption of civilization as we know it by our cousins across the water. However, recently I've been reading old newspaper reports from the early 1900s and have consistently found them writing color, honor, etc. I wonder if anyone knew when and why this changed.
Well, you missed off the connected question, why is the spelling of the Australian Labor Party using the 'or' form. Wikipedia is inconclusive on the topic. From what I read on it while researching the ALP it was either a homage to the US labor movement or it was a common spelling at the time.
I think it is probably due to editorial decisions at newspapers from that time because the same usage does frequently occur in Australian books from the same period. If anyone has a copy of any Australian style guides or editorial guidelines from that time I'm sure we could answer this question.
I have some dictionaries and books on writing from late 19th century so I'll update this later if I find anything.
Don't dismiss the inability of editors in small town and regional newspapers as a possibility either. Australia has a long history of incompetence in that department.
Update 1: I found this article which references an article from before Australian Federation (pre-1901) that blames the problem on the availability of American dictionaries. The article cites papers that I can't find online but they are probably hiding in some upstairs section of a university library.