I've been trying Andrew's recommended photo styles enclosed in the GH4 Guide. It seems that the "C3 - Flat" settings can cause banding and a red rainbowing effect on gradient backgrounds.
I'm also on DVXUser and we've been discussing the issue and trying to figure out what could be the cause. It appears to be the fact that Master Pedestal is pushed to +15. I'm both trying to report possible issues and figure out fixes.
Here's a screen grab of the shot: [Graded] - [Ungraded]
I also cooled down the image which helped a bit.