My identification is a statistical one in that, thus far, when I've seen a fungus with this sort of appearance in the ACT, it has turned out to be Perenniporia ochroleuca, a species that is widespread in the world. If I'm right it would have a tough, corky texture and pores on the underside. The intensity and extent of the yellow-brown colouration can vary. You can find it on both dead wood and on live trees. There are some superficial look-alikes elsewhere in the world and perhaps one day one will be found in the ACT.