Nice image Doug. Glad someones making the most of the odd clearish night
Did you try to realign the blue channel in registax? Or maybe try fewer images in your final stack. Be more discriminating in your selection by manually selecting only the very best images. You might find you end up with a "cleaner" image by only using 75 - 100 manually selected images rather than letting registax select the best ones. The down size of using less images though it that you can't push the wavelets as much.
You might also want to consider using
RGB splitter and PCFE as part of you processing routine and do the final colour combination in Photoshop or Astra Image (not free unfortunately). Check out Mikes planetary processing tutorial in the
articles section.