I visited Fort McHenry National Monument in Baltimore MD just about a week ago and took this picture of an original iron 4-pounder gun on a reproduction carriage. I will let you decide what shade of blue to call it. Fort McHenry "restores to" the 1812 era, for the most part. Therefore I am sure they've done their homework as far as what colors the artillery carriages should be painted. I'm sure they would share the information they have with you. Their very knowledgeable historian is Ranger Scott S. Sheads who can be reached at: 410-962-4290 x 244.
I found my photo of the Wurst Wagon caisson at Morristown Museum, and although the photo leaves something to be desired for lighting, I could not see any paint, only bare wood.
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