I have started weathering the SCT stock for Barcoola,
This includes two Auscision SCT class locomotives.
First, all the panels and grilles were black washed, using Humbrol paints a mix of matt black #33 matt grey #64 and a touch of grimy brown #98.
A wash of Grey was applied to the foot plate,
Then I mixed up True Color paints, TCP-174 Grime, added TCP-005 White, a dash of TCP-173 Weathered iron oxide, and TCP-070 reefer Orange, this gave me the right mix of grime.
A word of warning, do not use their Grimy Black, for some reason it has green in it, just does not work.
The reason I do this is to give you more control in "dusting" with repeated passes of the gun, you can get very good control of the paint, as the application is very light.
SCT001 has been dusted, and its fairly subtle, just compare it to SCT002, which is out of the box with the grilles picked out.
Here is the prototype shots I worked from.