Here are some samples from a recent dive showing the halo/banding effect that has been mentioned. This was shooting without a filter. I manually white balanced on a grey slate as I was descending at around 25 feet. I don't recall the temperature that popped up, but it looked good at that depth. I then descended to about 50 feet without touching the white balance. I've used this method with other sony cameras (EX1R and Z1) and while it's not ideal (images are fairly blue), the results are usually acceptable and can easily be corrected in post. This was shot with a 1080/60p PS setting, 0 db Gain, and everything on manual. The effect seems worst in darker areas at F stops of 16 to 13. You can see them come and go in the video clip as the image becomes more exposed and then darker again. You'll notice me adjust the iris manually from F16 to F13 aat around 15 seconds int0 the video clip.
I originally thought the banding was some sort of reflection inside the dome port, as I have had issues with that as well. Silver is a bad color choice for a lens. It's interesting to hear that the effect has been seen topside, as mentioned on this thread about the FS700.
Under what conditions are you recreating the halo/banding effect topside Simon? Seems like it would be easier to experiment on the dry side if that's possible.