Very interesting.... Early April 1940, NX1aaaa (a being a number !) a chap born in regional NSW, in a town on the Lachlan River, travelled by train to Central Station, Sydney to enlist. He asked at Central, and was informed to go to Victoria Barracks, so he walked there. (this is oral history from his son, who went to school with one of my younger siblings). He signed up at Victoria Barracks, and the form was P I N K ...
Son knows this because his Dad told him so, and his Dad had added, Victoria Barracks was allowed to use PINK as it was the headquarters, and the Sun never sets of the British Empire which is PINK on all the maps.
So, I am basically sharing some urban myth, but I have just now checked the naa.gov.au and .... yes there's the digitised B883 file for that chap. He was a Private, 2/13 battalion, (Tobruk), POW
I will send you a PM with his NX number. - Yes, there's that form in that file and yes, it is on PINK paper.
JM