For what it may be worth, the Spaniards had regulations to paint ordnance a particular blue-gray, that contained a cobalt oxide from Andalusia for a distinctive color. Again, the Spaniards published their ordnance regulations just as the U.S. did with the olive drab of 1840s-era gun carriages or "cureñas" in Spanish. Determining what color was used by the post-Independence Mexican army is difficult. Some Napoleonic-era British carriages, for example, may have been left in the British gray. U.S. ordnance in the Revolutionary War was apparently painted any number of colors, but after the French intervention came to be a sort of light blue or Prussian blue or whatever.