Eli5: How do photo restoration artists know the supposed colors of greyscale images?

Question

Are the colors based purely on their assumptions/imagination, or do the greyscale images retain some sort of data that tells what color on what part?

In: 641

Answer 1

https://youtu.be/vubuBrcAwtY <—- I remember a Vox that explores this topic on recoloring old photos and its super interesting! Lots of researching and lighting principles to get colors that are as accurate as possible.