One thing to keep in mind is that the dye used by the French to replace Woad for Dark Blue during most of the Napoleonic wars utilized Indigo. This dye stuff varies quite a bit in shade from light to dark depending on a variety of factors in the dying process, but the hue is always toward the green end of the spectrum, as opposed to a more purple shade of say Ultramarine or Cobalt.
This is the exact same recipe used by suppliers to the Union Arsenals to dye Federal Uniform cloth during the War Between The States.
Incidentally, the short period during 1806 when uniform coats were changed back to white was due largely to the short supply of Woad natural dye. Once enough Indigo from the Americas became available, the French returned specs to the Dark Blue of the post Revolution/1st Empire.
