Thanks for the link. Quite interesting.
The hand coloring technique is interesting. Multiple color tinting is almost the exact same process in digital photography. Occasionally I do some simple tinting in my photos using two or three color layers, but I've seen examples were people have used up to ten different tints to colorize a photo. A similar process is to convert a picture to black and white then put some color back in by laying a copy of the original color photo on top of the black and white and selectively reapply the original colors with masking and adjusting layer transparency.
I think the results are often quite interesting.
