In other words, bullshit.
That's what happens when you are filling in missing info that isn't in your source.
EDIT: Of course, color photography can be “bullshit” rather than accurate in relation to the actual colors of things in the image; as is the case with the red, blue, and green (actual colors of the physical items) uniforms in Star Trek: The Original Series. But, also fairly frequently, lots of not-intentionally-distortive reproductions of skin tones (often most politically sensitive in the US with racially non-White subjects, where there are also plenty of examples of deliberate manipulation.)
But, yes, in general inaccurate color reproduction can be intentionally manipulated with planning to intentionally create appearances in photos that do not exist in reality.
For some it’s more evocative, irregardless of the absolute accuracy.
Having a professional do it for that picture of your great grandad is expensive.
Having a colourisation subreddit do it is probably worse for accuracy.
I think there is a place for this bullshit.
So bullshit is the best you're going to get.
Should artists not put their bs in the world? Writers? Musicians? Most of it is made up but plausible to make you feel something subjective.