I think this is more likely to be Crocanthes glycina which has been recorded commonly in the ACT. C prasinopis is more northern, although it has been previously recorded on Black Mountain. C. glycina is yellow and black, matching these photos, whereas C. prasinopis has a bronze hue. C, glycina also has a more prominent black costa on the forewing. The dark apical mark is plain on some C. glycina specimens, and hollowed out yellow in others, like this one.