Exercise-track ink leaves an archival uncertainty

Exercise plots recorded the tracks of opposing forces, sometimes using blue ink for the blue force. Some surviving documents instead show black or slightly different shades of black. One proposed explanation is that blue ink changed colour, with saltwater exposure and later storage considered possible influences. Paper specialists considered colour change possible without settling this case; the alternative is that a different black ink was used originally. A colour visible in a surviving plot cannot automatically be assumed to match the original force marking.