I've used Vegas Pro's colourisation AI FX a couple times with good results. And I've seen on YoutTube a lot of late 19th century and early 20th century B&W video that have been stabilised and colourised - but often the colourisation results in small or larger areas of the video image being affected by brown, blue or purple tinging making the result somewhat unrealistic. But the History Channel has just telecast locally a series called "Edwardian Britain in Colour". The colourisation is exceptional - no tinging at all. An example is:

... though I had to use my phone camera for the above because PrintScreen and the Snipping Tool only recorded a blank image. A few of the colourised images so close to realistic that you wouldn't think that they were colourised. Throw in the likelihood that the original camera footage was filmed at the then standard hand-cranked 16 fps.

I've never seen better colourisation than in this series.

As an aside, I wonder if Bird's Custard Without Eggs is still on the market in the UK?