There is a community of people who carefully recolor historical photos by hand. It's really beautiful time consuming work and often they invest heavily to get the colors to be correct.
The effort is obviously going to be less accurate.
But it reflects the fact that an accurate colourisation of a black and white image without access to every possible detail about the scene and processing from the photographer's perspective is impossible.
Black and white film is substantially more complex and varied than people understand. Its sensitivities are complex and vary from processing run to processing run, and people at the time knew of the weaknesses of black and white and often used false colour to get an acceptable rendition.
Colourisation is a form of expression, not a form of recovery.
>But it reflects the fact that an accurate colourisation of a black and white image without access to every possible detail about the scene and processing from the photographer's perspective is impossible.
Accurate colourisation is impossible even in a color photograph. There is no "canonical" film stock that accurately represents all actual real-life colors.
The expectation from colourisation is not an accurate representation of the original colors, but a good application of color based on our knowledge (whether from historical facts a human colorist knows or from training with similar objects and materials a NN did) that matches a realistic representation of the scene.
If a human colourist draws a dress and doesn't know the color of it, nor have they any historical information about what the person depicted wore that day, they're going to take a guess. That's kind of what the NN will do as well.
What if the "effort" way is less accurate?