Very shiny metallic blue. It hopped. It may have been under 5mm. It was pretty small. I think 'flea beetle' as a description is in the right ball park. Arsipoda might also work though.
Judith, there are a couple of species of Altica recorded from the ACT, but they are difficult to separate in photos, so I will call this simply 'Altica sp.'. The name that you suggested, Altica pagana, is a synonym of A. corrusca according to the Australian Faunal Directory (AFD).