Yep the purple flag is in use across all disciplines of junior competition here in NSW.
The thing to remember is that the flag can only be used by the junior competitor and can not be used once an adult has come in contact with the rider after the race. The flag is usually placed at the entrance to the pits.
I can say that I have only ever seen the flag used once in the last twenty years and that was at minikhana and was a dispute over the rider being fouled out in a bending event.
Seniors of course rarely use the protest system possibly because of the associated cost of doing so.
Maybe we can take some pocket money off the kids for unsuccessful protests
Cheers
Shaun