The 1d was was the concessional rate for troops' letters. The 2d was used for (a) the letter rate within Australia and the British Empire; and (b) the postcard rate to foreign countries. The 3d was (a) the registration fee; (b) the airmail fee within Australia; (c) the letter rate to foreign countries; and (d) the commercial papers rate to the British Empire. And the 6d was (a) the parcel (Scale 1) rate; and (b) the forces' parcel rate.
Left - Right: Greyish Green, Bright Yellow Green, Green
Left - Right: Scarlet, Bright Scarlet
Left - Right: Blue, Bright Blue
Left - Right: Purple-Brown, Deep Brown
The deep brown shade of the 6d has a slight aniline quality, and has a tendency towards ink stripping.