If you want them to look like Australorps (with single combs), start with a colored egg layer that has a single comb (example: Cream Legbar.)
There is a link between the gene for blue/not-blue eggs and the gene for pea/not-pea comb. They are quite close together on the same chromosome, and tend to be inherited together.
So if you cross an Araucana to an Australorp, you will find that their descendants almost all fall into two groups: pea comb birds that lay green eggs, and single comb birds that lay brown eggs.
But if you start with a single comb bird that lays blue or green eggs, then you can use it to breed more single comb birds that lay green eggs.
Since Australorps lay brown eggs, you will probably end up with a bird that lays green eggs and not blue eggs.