Like all theatres and periods, gun colours are contentious. As my namesake says, taking colours of Museum examples at face value is likely to be incorrect. Many pieces had long service lives and went through numerous hands and potential changes in livery.
In my own area of expertise Sikh artillery of the Sikh wars were actually documented in light blue with red lead fittings and natural wood with blackened iron and/or bright brass fittings. Most preserved painted carriages are in ubiquitous War Dept battleship grey with black ironwork repeatedly slapped on over the years to prevent rot and corrosion.
Factory fresh munitions were likely to be in the livery of the dominant client of the manufacturer. Thus pieces contracted by a manufacturer for supply to the US army would most likely have left in US army green and from German suppliers probably in a field grey. The longer they were active service overseas the more likely they would have had a lick of whatever paint was to hand but this was usually to prevent bright metal spots or corrosion developing. Field pieces tended to be held back from front line service and/or emplaced where blending in or camouflage was not such an issue. Camouflage primarily developed to evade spotting and aerial observation so likely falls outside the scope of the MexRev period.
This whole study is not helped by the absence of colour photography to record the livery accurately and we are reliant instead on documentary evidence and photo interpretation (not easy with the earlier photo processes that were employed).
