Someone has written a bot which automatically colourises photos that are sent to it via Twitter. This is what it did with a photograph of the Darualman railway. Note that this is just for fun, and it is not intended to be historically accurate!
A photograph of the Kabul to Darulaman narrow gauge railway that I hadn’t seen before. The person who suplied the image didn’t have any information on the source or date (presumably the 1920s). The Darulaman palace is visible in the background.