Unfortunately
https://colourise.sg/#colorize will close on Oct. 1, 2020.
It was the best colorizing website I found.
This is the second best colorizing site I found, mediocre colorizing.
https://photomyne.com/colorize-app
There may be better sites out there. Try some of them, maybe you'll get better results.
I used the BW photo of Natalia Andreeva to test all the sites.
I tried about 10 online colorizing websites, most of them gave poor results.
There are some free apps you can download to colorize, but the best apps you need to buy.