Well, I've seen plenty of cobalt blue medicine bottles from the Civil War era, and they're still blue, 150 years later. The professionals who are conserving the Hunley and her artifacts agree that the lantern which they found on the sub has a clear glass lens, and existing antique lanterns of the same design all were manufactured with clear lenses, not blue ones. If you believe that at one time it was a blue lens, and that the minerals which made it blue have disappeared in 150 years, leaving clear glass, then you could argue that the Hunley crew took an oil-fired, wick burner lantern into the sub with the intention of using it to signal to shore, four miles away. Period experiments had shown that putting a blue lens on an oil lamp decreased the light output to one seventh of what it was with a clear lens; Dixon would have been an idiot to use the worst possible colored lamp to attempt to signal to shore. That's why the military didn't use blue lamps to signal. That's why the lights on fighter planes in WWII were blue: your wingman could see your wingtips in formation, but the enemy fighters couldn't see you at a distance. Blue is poorly detected by the human eye, so it makes a poor nighttime signal. It's pretty clear to me that the blue lantern is a myth, but if you have any evidence to support it, you'll be the first.