There are few ways to colour b/w photographs. One is, of course hand colouring, that is to buy some photo colours and paint on photograph. Easies way are Tetenal's colour pencils, you use them like pencil colours, no needs for mixing colours. There are three sets of 10 or 12 pencils with different colours and shades in each set.
Next methods are unfortunately digi.
Scan b/w photo, paint it on PC and print it.
And, then, few years ago I was reading about Russian software which is used for restaurating old colour photographs where colour faded away or to colour b/w photographs. I saw samples of job on some really old photograph which Russians wanted to restaurate as national treasure, and was extremely impressed with results. But, unfortunatelly, it is not public software, it was invented for resturation jobs, and was not on market for selling at time I was reading about it.
And, as I remember, Israel software programmers made software for colouring b/w photos too. There was even free source code for download, and results were good too.
But, as I am not interested of doing digital photography (just to know about enemy to fight it

), I don't remember anymore where to find those softwares ...