Australian? Well, I can just forget about paint scheme trends over time, as all those I know apply to the US and Canada only. I noticed that all the versions of the scheme slightly resemble this http://railpictures.net/viewphoto.php?id=156073 QRNational scheme. Since your line operates in present-day Queensland as well, perhaps some change should be made to make the scheme less reminiscent of the competitor.
Mitchell, I stumbled across your post and thought I'd add a little note to the discussion. I've taken your initial design and tweaked it a little although the body used is a SD60M but close enough to provide visual representation. As you can see I've added a white accent line between the orange and dark color to provide contrast. The arch created by the dark color on your original scheme struck me as interesting so I tweaked the front to visually carry and reinforce this arch from roof top to sill. The addition of a white outline on the road number and GTRail name carries the white accent through. Finally the fuel tank and trucks (not shown) would be in a silver/metallic paint similar to Santa Fe locos and UP Heritage units. Hope you find this helpful.
