The question of what colours was used on the War Machines of WW1 is a constant
problem. The Standard French, German, British and Russian colours are pretty
much nailed down now. That cannot be said of the colouring of the heavy
equipment of the Austro-Hungarian Army. The crux is the same as with any WW1
army colours: there are only very, very few colour photographs (and interpreting
black-and-white photographs regarding the correct hues is almost impossible) and
many times the surviving pieces of equipment have been repainted.
Here I have gathered some
photos of surviving pieces of Austro-Hungarian guns from WW1. These have been
chosen because they all appear to have their original coat of paint.
From these, it appears that two
principal types of hues were used. Note that there are shades within these
principal colours, depending either on the different fading that these types of
equipment have been subjected through the years, and the different batches of
colour.
First, a somewhat pale olive
green, with a hint of
brown in it, thus:

The best approximation of this hue, when it comes
to model paint, is probably the Humbrol no 159, Matt Khaki Drab, or Humbrol no
105, Matt Marine Green.
Secondly, a light leathery
brown, a bit of khaki
mixed with nut and a bit of brick-red, thus:

The best approximation of this hue, when it comes
to model paint, is probably the Humbrol no 62, Matt Leather. This seems to have
been the most common mode of camouflage.
Thirdly, patches of
light green and sand yellow over light
brown, with the green
patches dominating, and together with the yellow patches forming a sort of
segmented camo, thus:

This camo with all probability is
a development from camo no.2, the overall light leathery brown. New colours are added by brush.
These are just simple suggestions, based on these
surviving pieces of WW1 equipment. If anyone has any new information or
correction, do not hesistate to send them over!