GGR from Image

[Ofnuts]

Try this:

• Open the palette editor (in the Palettes list click the "Create new palette" button
  
• Color sample each band in turn, then clikc the + button in the palette editor to add it (the ruler is my screen ruler app that I used to keep track of where I was)
  

   

• Give a name to your palette. It should appear in the Palettes list
  
• Right click that palette, and Color to gradient
  
• In the Gradients list, you should now have a Gradient with the name of your palette
  
• Create a rectangular selection on part of your image
  
• Set the active gradient to the one sampled from your palette
  
• Start the Blend tool and drag the gradient across your image
  
• Adjust the stops (more or less in the middle of their bands) so that the bottom is aligned to the top (yes, I probably missed a color on the right)
  

   

• At the top of the Gradients list, right click the Custom gradient (which is the one you creating on the fly), and duplicate and rename it