Andrew
We just returned from Cinegear today to find these posts and the others you left today, so forgive us the few hours to respond. The top-to-bottom hue 'gradient' looks more like interference.
If you rotate the achromat (which I know is a bit tricky if it's completely setup, but just turn it a little bit) does the color banding move as though it's part of the achromat?
If that doesn't change it, try moving things away from the camera (monitor, magnets, anything electro-magnet, etc.) and see if that helps. Perhaps move it into another room?
Cheers
Brian