Colourised images absolutely replace mono images in image searches, unfortunately; I've seen this again and again. It gets more difficult to find originals.
But also you have to consider that bias is being introduced in the colour rendition. That causes damage.
For example, you could see a photograph of an African American woman in the 20s or 30s, and your AI would say, this is an African American woman and colour her skin in some way.
But a lighter-skinned-looking African American woman in a pre/early-post-war photo is a challenge. She may have had darker skin -- been unable to "pass" -- and the film simply didn't get that across because of its colour sensitivity.
Or she may actually have been light-skinned and able to "pass" (or wearing makeup that helped).
Automatically colouring that image introduces risks to the reading of history; you can read that woman's entire life completely wrong.
It's also common with photos of men from that era who worked outdoors. Many of them will come across much darker-skinned in photos than they actually would have appeared in real life, because not-readily-visible sun damage can look odd in mono. But if you colourise all those sun-baked people the same way, what happens to those of mixed heritage among them? (A thing that is already rather "airbrushed out" of history.)
Without knowing about the lighting, the material, the processing and the source of the positive (is it a negative scan? was it a good one? or is it a scan of a print?) you cannot make accurate impressions of skin tone.
And given the power and importance of photography in the history of the USA in particular -- photography coincides with and actually helps define the modern unified US self-image -- this is not something to blaze through without care.
This is a far less tricky problem in more homogeneous societies, obviously. But even then, there is this perception from photographs that British women in the 1920s were all deathly pale; colourisation preserves that illusion that actually comes in part from photographic style.
