I'm still learning GIMP. It's not self-explanatory or intuitive when playing about with tools. Wikihow has written and video tutorials and I've just looked at HOW TO Colour Hair. It's comprehensive but to my mind it's a poor tutorial because it tries to cover all aspects of the job at one go. Paint.net's tutorials are simpler, step by step.
However, the first part of Restoring is to repair the damage and that can take most of the time as the colouring is Child's play using a Layer which you Block in the choice of colour solidly and then adjust the Opacity / Transparency of the Layer as an Overlay on top of the original Image. When you judge the result to be satisfactory you Flatten the 2 Layers into one, they have been Merged and you can Save ( or Export in Gimp) as a PNG file, or a Jpeg if you want to drastically reduce the File Size, but you will lose Pixels and Quality.
GIMP's clone stamp can be used to carry out 90% of damage to a Photo. By using a Clone Brush of a suitable Size you simply Select a GOOD area of the photo as close to the damage as possible and Stamp on the selected Damaged area. ( You are effectively Copying one selected area and Pasting it over a damaged area).
In paint.net I select the Clone tool, select a suitable size, adjust the Hardness to around 20% for smoothest edges then select Anti-alias. Then it's a case of changing the area to be copied to cover the damaged area. It's the same in GIMP.
Copy the Image of Father Ryan to experiment with as it's an excellent Black and White candidate for Repairing ... as evidenced by the posted results.
cheers, Ian
