Can't claim to be an authority on this, but I can tell you what I've seen in depictions and a couple of titbits I know. Paintings, colour plates (and a certain movie with a famous drunken road warrior) show both white shirts and the British greyback style being worn.
If the figures are light horse in bandoleer equipment, that will be leather. 1908 pattern webbing would be "khaki", but I have seen this vary from a light sand to a bright green. Take your pick. Also, due to a shortage of webbing, some Australians were issued with leather equipment modelled on the 1908 pattern webbing. So you can paint the webbing as leather instead on Aussies if you prefer.