I stumbled across a project to convert black and white photos from Indian history to colour using machine learning based colourisation:

History in Color contains 1200+ Old and Historic Photographs of India from (1800s to 1940s) restored using advanced image processing techniques and colorized with deep machine learning.

While the colourisation isn't totally realistic, it makes the details pop in a way that black-and-white just can't.

Here are three photos I found most noteworthy, each from almost 150 years ago: