These are orts from blue-gum nuts, after gang-gangs have fed on them. I think that, similar to allocasuarina orts guiding observers to the presence of glossy black-cockatoos, the colour of the blue-gum orts are a clue to how recently gang-gangs fed in an area. The whiter the ort, the fresher the visit from the gang-gangs. The older orts gradually colour with age, to a darker, duller brown/grey. The first photo gives, I think, an idea of freshness of gang-gang feeding, moving from the left (nut itself, then newly chewed husk, then maybe just a couple of days old etc, down to perhaps months old, which is grey/dull brown).