Color Migration

Intention
This post describes a simple effect to produce images with (discontinuous) color variations, as can be seen below.










Summary
We basically use several layers containing the original image and the modified images. This may or may not involve masks.


Steps

1. Open the image; name it e.g. "original" layer
2. Select an area on the image whose color you want to change; continue with [Edit]-->[Copy]
3. Add a transparent layer; name it e.g. "var1" layer
4. Click/activate "var1" layer, then [Edit]-->[Paste]
5. Apply a "color" effect to var1 e.g. [Colors]-->[Invert] or [Colors]-->[Desaturate]
6. Repeat the steps 2-5 to make another "discontinuity"
7. You may also do the steps above with masks: duplicate the "original" layer, name it "var1a" then apply step 5; right-click "var1a" layer choose "Add Layer Mask" (use white color for the mask); apply step 2; activate the mask on "var1a" layer; fill the selection with black color (e.g. [Edit]-->[Fill with FG Color])
8. If you want to have a smooth transition between colors, try [Filters]-->[Blur]-->[Gaussian Blur] on the mask
   

Note
GIMP 2.4.6