Left is a Western Ground Parrot, a breeding adult male, photographed by Brent Barrett. The iris is a golden colour with a slightly paler inner ring.
Right is an adult Eastern Ground Parrot photographed by Rohan Clarke showing a white iris as described below in (3).
The full series of age-related changes in the iris colour of the Eastern Ground Parrot is shown in Table 4 below. The full series of age-related changes of the iris colour of the Western Ground Parrot has not yet been described. Certainly the adult bird's iris colour differs from that of the Eastern Ground Parrot.
McFarland was able to make the table as he retrapped birds on many occasions.
The text is copied from McFarland, D.C. (1991). Flush behaviour, catchability and morphometrics of the Ground Parrot in south-eastern Queensland. Corella 15, 143-149.
The photo (centre) by A. and R. Smart, is a Western Ground Parrot (WGP) fatally injured by a vehicle. It is a mature female and has a pale iris. From these and other photos of WGPs it seems likely that the iris of the WGP pales over time, but not as rapidly as that of the Cooloola Queensland Ground Parrots. This bird is now part of the Western Australian Museum collection, no. 27142.