The Sydney Morning Herald – under the headline, "Are You Wearing Khaki Today?" – reports that the idea started with an e-mail campaign by Aussie environmental engineer Andrew Tapsall.
Tapsall said his wish was to remember the "late great" Crocodile Hunter star, who was rarely seen in public without his trademark uniform of a khaki shirt and shorts.
The tribute, Tapsall tells the paper, "is not about raising funds for wildlife. This is all about commemorating his achievements. Through his entertainment, Steve Irwin was educating everybody, without them even knowing they were being educated. It was almost subliminal."
Irwin, 44, was killed Monday when speared by a stingray barb while filming a documentary off the coast of Queensland.
His family plans to hold a private funeral possibly next week, reports say, while a large public memorial service is in the works for later.