
British
Artillery during WW1 could be seen in the following schemes and/or combinations
of colours (the names of the schemes are my own invention, and are intended for
simplicitys sake only):
A.
Overall Blue-Grey
This is the oldest type of scheme, probably a left-over from the traditional way
that British Artillery was painted during the 19th Century. It could be seen
used on guns at least until 1917.
B.
Overall Khaki
This scheme was introduced around the turn of the Century. The khaki was "a
light browny-green". This was probably the most common camo on guns at the
start of the war.

C.
Overall Mid-Green
This colour and scheme was introduced first sice the hostilities started, and it
is a fair assumption that this was the most common camo used on British
guns, vehicles and big pieces of equipment during the duration of the war. The
exact shade of this colour is not known - and will never be, as colours in this
time could vary a lot, both due to production variations, and due to the effects
of weather, aging and wear. (It is quite possible that this mid-green in reality
was TWO different shades: we know that the colours most commonly used by the
Royal Engineers for camouflage during WW1 was "Light Brunswick Green"
and "Dark Brunswick Green".)
D.
Dark Brown Blotch over Mid-Green
This camo is just this: Dark Brown in large Dark Brown blotches over the usual
Mid-Green base. This seems to have been most in use during the years 1915-17.
E.
Multi-Colour Dazzle Camo
During WW1 the British, like most other Armies, also used some very spectacular
so called dazzle camo, in the British case consisting of angular, irreglular
segments of, most commonly, three colours: one very bright, most probably a
light creamy yellow (that might, just might, in some instances be white); one
dark, with all probability mid-green; plus finally one even darker, probably
dark brown (the same used in the Blotch Scheme), but possibly dark green, but it
might, might, even be the old colours of khaki or blue-grey.

F.
Multi-Colour Segment Camo
This can be seen as a variation on the standard Dazzle scheme. In this long and
pretty broad bands of a disruptive colour was painted over the base colour (most
commonly, of course, mid-green, but other base colours were of course also a
possibility, like Blue-Grey or Khaki.). The disruptive bands were in general
painted in a wavy, and vertical manner. The colour of the disruptive was in a
contrasting shade, like Khaki over Blue-Grey, or Dark Brown over Mid-Green. In
general, the broad bands were separated by thin lines of highly contrasting
colour, most commonly either light creamy yellow or black.
Main
Source: "British Artillery 1914-19 - Field Army Artillery" by Dale
Clarke nad Brian Delf (Osprey New Vanguard no.94). If you are at all interested
in his subject you should really get this book. I'ts worth the price just for
the artwork alone.