fastpitch17 uses Photoshop and a technique refined over the years to colorize old black and white photos and paintings or drawings.
It is much more complicated than it looks: apart from the technical skills to actually “color within the lines” with Photoshop, a great deal of research is needed to find out what the original color is supposed to be. For example, with skin tones, fastpitch17 has created a color palette matching skin tones from various ethnic tribes based on research of his own and using modern day footage. Sometimes, it involves researching through old news papers and books describing various objects in the photographs in order to figure the colors. And sometimes when no information is available, it is down to instinct.
Head over to the thread on Expat Indo Forum to learn more!