I’ve done photo restoration for a bit over a decade now, and there’s a few tricks here. The biggest one for me is research; with a little research it’s not hard to find out what colors certain things were exactly (uniforms, cars, buildings, etc). Adding onto that, colors have popularity over time, and knowing which colors were popular when/where help a lot at guessing what a color is.
When I’m *fully* stumped on a picture, I’ll shoot it over to my grandmother and her and her friends usually have a good idea of what the colors were. If all else fails, I just assume what the colors are based on the lightness/clarity of the greyscale and the context of the image. Though I do prefer to have some kind of confidence in the colors I use in a restoration, so I try to guess as little as possible.
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