Ipsom, funnily enough, its the bird life that provide most of the colour in the tree's here
and yep, not that their all due to leaves, Jacaranda's (purple/blue) (not native, but thrives and very, very common here, almost a native by default now) Crimson bottlebrush (for red) (and banksia's, protea's ect.) and golden wattle for the yellow, provide most of the tree colour in this part of oz. and its as mentioned spring/early summer this all happens.