Re creating these type of images is very difficult.Each and every pixel is coloured and seperate layers of each portion is made during work.
I remember i took me 2weeks to color two old pictures,the simple key to success in re-making these pictures is Higher Resolution Scan.The higher the depth of scan the greater the results.
It was my plan to colour some old PAF hisoric black & white shots but unfortunately i don't have that much time these days...may be in future
I try to go at least 3600dpi and then use Digital Image Studio ( Microsoft's answer to Photoshop) and increase the saturation. You start to see detail you could not before. Some of these pictures are really early (pre ecktachrome) color photos.
If they are early color photos then giving them new life isn't a hard nut to crack...it is difficult but coloring a typical black and white picture with lower concentration of pixels is even more difficult!