I haven't had much restoration work to do lately, but here's one:
Technically speaking, a job like this isn't very difficult. But there's a certain amount of educated guesswork involved in picking the colours. I can't be sure exactly what colours the clothing and backdrop are meant to be, and my client wasn't certain either. In that case, I just needed to be satisfied that I'd achieved a pleasing result.
In fact, I like to think that in a lot of cases I achieve a result that looks even better than the original did many decades ago!