I don't either! That is what Google is for! :D
I stole this pic off of a site that claimed to be breeding winning show stock, so I assume this is a quality Blue Australorp:
Well, you know a heck of a lot more about chickens than I do, but in every picture I've seen of blue roosters of any breed, the back, hackles, and saddles are much darker than the belly. The hens always look a bit more uniform except for a darker blue head. You sure the "dark wash" on theirs...