[OT]Aussie colors ?

A question to our Australian friends.

I have been watching the Olympics (congratulations to all those winners
out there!). 

The sports dress of most nations'  teams include the color of their flag
in their design. 

Strangely, the Australians wear green and yellow, which do not appear in
their national colors. I also have seen fans decked out in green and
yellow. 

Can somebody from down under enlighten me about those colors ? I guess
it is not just the whim of a designer ?

Greetings
Karl Heinz