From the Official Army Colour Patch Register;

The triangle has a 2" base and the other two sides are 2 1/4" long.
The colours are Light Blue, Red and Dark Blue.
The Dark Blue band is 1/4" wide and the Red bands are 1/8" wide. There is no surrounding colour.
These patches were made from felt and should be warn on both shoulders.
The AFC Patch was authorised by D.A.G. A.I.F. 15/67 of 10 July 1917.

All AIF formations had these patches in both World Wars and they have reintroduced them to the current Australian Army. The colour and shape of the patches were authorised in a consistent pattern during Wolrd War I, but World War II the consistency was lost to an extent. It was possible to know during World War I which unit, such as Battalion, Regiment, Brigade or Division a soldier was serving with, by looking at the patch.

	Australian Army Patch for the Australian Flying Corps.
	Australian Army Patch on Lieut Jack H. Weingarth while training in England, 1918. The triangular shoulder patch is clearly visible on the right hand shoulder of the uniform.