I recently discovered that my tutorial on Gimp Chat for colouring photographs was incomplete and I no longer had a copy on my computer,
Fortunately, I was able to come to Gimp Learn and download it.
When the tutorial was written it used overlay blending mode for the colour layers (overlay, at that time was the same as soft-light). Now they are different I find that soft-light gives better results and is more controllable.
Just to prove that it still works and I am capable of doing it, I have coloured an image of Grand Duchess Olga Romanov. The lesson from this was to avoid subjects with pearl necklaces - they are a nightmare to mask!