I had only thought about the sensor because I had been shooting long exposures all day, though none of the other images from this shoot exhibit this kind of discoloration. I had shot basically the same frame with my 40mm lens too, and there is more fogging, but it neutral in color.
Anyway, after find the gimp dev PPA, I got 2.9 and applied the chrome fix as @Morgan_Hardwood suggested. Worked like a champ.
Here is the image:
Many thanks for the help; looking forward to gimp 2.10. Hopefully it will make it into the Debian Jessie backports ;D