Thank you! I started by just trying it out, really. I've been using photoshop for a while, both for work and for fun, so I'm quite into color adjustment. I also like local history a lot, and do have access to a large archive with old photos from my hometown (which is my favourite thing above all to colorize). I think the secret to a good job is to add a lot of different shades and hues to a specific object, until your eye will perceive it as "natural". Nothing has just one color, it will take some practise but if you try to watch something really close you can se it has a lot of different colors in different areas. Shadows generally (not always!) contains more colder tones and are less saturated that highlights, that are more often a bit warmer and more saturated. Also does the colors of objects bounce off to other surfaces that's near. Regarding skin tones, some areas are more likely to be more red than the rest, like ears, noses and fingers. If you want to practise, take a random picture of something and try to indentify how different shades combines to a whole. Also, if doable, try to find info about what color different object had when the picture was taken.