This script creates small rectangular selections and auto-white-balances them.
Copy it into the scripts folder from GIMP, you will find it then under Filters -> Light and Shadow -> White Balance Puzzle.
Be careful with the feather option, it consumes a lot of cpu power.
I use it more as an analysis tool for existing images. You can detect edits in low contrast areas with this script.
This script gives a strange result, so it just fits in rare conditions:
If you like this script, hug someone.
For all scripts together, go here: