2021 Aboriginal flag $2 paint upset
The Royal Australian Mint's 2021 mint set included a coloured $2 coin commemorating the 50th anniversary of the Aboriginal flag. The reverse had the legend AUSTRALIAN ABORIGINAL FLAG 1971 above and AUSTRALIAN ABORIGINAL FLAG 2021 below with black paint at the top and red paint at the bottom.
The Purple Penny have reported finding a mint set with the Aboriginal flag $2 having its paint applied upside down i.e. rather than black paint at the top and red paint at the bottom the coin has red paint at the top and black paint at the bottom (p22, Nemtsas and Harris, 2021 Coloured $2 Coin Error in Aboriginal Flag Mint Set in Australasian Coin and Banknote Magazine, July 2021).
So far only one example is known but it is unlikely to be the only example of this error. It can easily be spotted - on the error coin the 1971 is topped by red paint and the 2021 is topped by black paint while on the standard coin the 1971 is topped by black paint and the 2021 is topped by red paint.Update:
A paint upset $2 coin has been found in a 2021 proof set (p32, Nemtsas and Harris, 2021 $2 Aboriginal Flag Misaligned Paint Update in Australasian Coin and Banknote Magazine, February 2022).