There's the Eastern, Western, and Northern.
Easterns have a pink/red eyering.
Westerns have a white/grey eyering.
And Northerns have a very bright red eyering.
There seems to be a wide variation too, taking into account male vs female, as well as the fact their eyering size and colour can be affected by sunlight, diet etc. It's hard to find solid info tho

Hence why I tend to avoid subspecies, that was just a fact I came across when I was actually researching eyering colour change in my galah

Other factors used for sub species identification are crest colour, slight variation in body plumage colour, as well as size, I believe.
Thanks!