Do you think it's possible that the violet shading is the result of contamination in soaking?
I had a quick look at the example sheet and die-cut versions of this stamp on Stampboards and neither shows the violet shading. I also don't see any shading on the other stamps that are shown there from the set.
Your AFL footballer came from AP's 2016 AFL team stamp pack for Collingwood (yuck!) issued in 2017:
With the start of the 2017 AFL footy season comes a fantastic range of licensed stamp packs, one for each AFL team. Released on 30 March 2017, to coincide with the Melbourne 2017 International Stamp Exhibition, these packs are the ultimate collectable for footy fans and keen statisticians and historians of the game.
Each pack comes complete with 20 $1 stamps from the Love to Celebrate 2016 stamp issue, as well as 20 current player images in the stamp tabs. The packs also contains a 2017 team playing list and interesting team statistics tailored to each team – from winning margins, premierships and club records to individual accolades, where applicable, such Brownlow medallists, Norm Smith medallists and club best and fairest awards.