Hello Grotuz...Force Publique and Belgian Congo are among of my favourite wargame armies/periods...i played a pair of historical games with FP minis (Vs African tribes and vs Madhists) and always enjoyed..among my sufficiently reliable sources i only find this image from J. Thiriar of a FP gun in action and in colour....probably your assumption of a blue grey with metal parts blackened or left in natural colour is the closest to reality....by the way how do you organised the carrying of the gun?....from my researches, as we are speaking of small mountain pieces, it would have been impossible to use anything different than human bearers with piece's components splitted among various carriers..in this very pict we can see on the left, as a small proof of that, a pair of bamboo rods similar to those employed by bearers with a box..probably containing tools or rounds...i must say that i never read anything specific even among my first hand Belgian sources...by the way i also never found any image...even images or evidences from other nation's use of bearers for their mountain/screw guns ..i'm always looking for pictures confirming that