Is this an australorp?

[victoriasews]

I bought 4 australorp chicks in June and they were all black with the dabs of white, all looking identical. They are now 9 weeks old and one is gray and one has a rust colored neck. The other 2 look like genuine australorps. Can they vary in color like this?

 

[RoostersAreAwesome]

Looks like you have marans or marans crosses instead