Coloring Help

[Ofnuts]

With a crude luminosity mask:

• Duplicate the layer
  
• Colors>Desaturate>Luminosity
  
• Colors>Invert
  
• Open the Channels list, drag any of the RGB channels to the general list to make a copy of it
  
• Right-click the copied channel and Channel to selection.  You now have a progressive selection on the image where the dark pixels are more selected than the light ones, so tools will apply more to them and leave the light ones almost untouched.
  
• Open the Layers list, delete/hide the black and white layer, select the image layer
  
• Use Colors>Brightness/Contrast to bring out the kid's face, you will see that the light parts of the image are mostly unchanged.
  
• Select>Invert to have a progressive selection mostly on the "light" parts of the image (the raincoat)
  
• Use Colors>Hue/Saturation to add some saturation to the raincoat.