It is already spring in Sydney and soon will be more and more outdoor event in the city.
This month most colorful spring festival in Sydney will be Festival of the Winds this weekend. Head to Bondi beach on 9th of September to see lots of kits in the air.
Another event I would recommend to visit is Art & About Sydney. Art & About starts on 21st of September with opening party, with celebrations in Martin Place. A lot of different events and exhibitions to explore art around the city, in laneways, parks and galleries. Check it here for full list of venues.
18th Biennale of Sydney is still open until 16th of September with various performances, film screenings and other special events. Everything is FREE the public.