Civil War, WWI, WWII, Vietnam I consider the stopping point for colorizing. There is a huge responsibility when colorizing war/military photographs because trust me, someone will point out if you colored a uniform the wrong color, or medal ribbons the wrong color, etc.
You HAVE to be very careful and do your research. The last thing you want to do is put the wrong colors on Patton; consider that the end of your career. Make sure everyone in the photo has the right color uniform, and that even the ribbons for the medals are the right color AND that if a certain person is show in the photo his/her rank color is shown (if that makes sense). Every detail is important; if you’re colorizing a uniform from another country and you’re not sure – the internet is a wonderful thing. Social media is great, and people are willing to answer questions like that.
There are times you’ll run into actors dressed in military uniform and that will throw you for a loop (How many WWII films did John Wayne do?). Remember some actors, like Clark Gable, were in the military for a short time – just take the time to look up if what they’re wearing is a costume, or a real uniform. I won’t get into Hollywood and military outfits, that’s another post entirely. The only time I’ve ever colorized a uniform is Buster Keaton in his silent film The Navigator.
Hope this helps!