I'm not sure that the following information is responsive to your post on color photos from World War I, but have a look at the color plate inserts in British historian Hew Strachan's recent book, The First World War. He explains that the French had developed an early process (now lost) for capturing color. The pictures, which he apparently discovered in a French government archive, are really quite vivid. Also, his book is an excellent read.Thanks, Richard. To bring this back to the Civil War era, note that in 1861,
Scottish physicist James Clerk-Maxwell demonstrates a color photography system involving three black and white photographs, each taken through a red, green, or blue filter. The photos were turned into lantern slides and projected in registration with the same color filters. This is the "color separation" method.Wonder if those photos still exist and what the color quality was like.