Hi Chris, I reckon you could get this a lot clearer by adjusting the position of your colour channels. Your reds and blues are getting split apart - see the blue fringe on one side and the red on the other. This used to happen to me a lot when I imaged with a acro refractor or when imaging jupiter at too low an altitude (eg anything below say 45deg).
It's a pretty easy fix I think in registax though I haven't done it for ages and never in registax 4. There will be an option in the later combining stages where you can set RGB offset and so shift your colours into alignment - bit trial and error but once done your pic will be considerably sharper and better colour balance.
Perhaps someone who has better recall that me could chip in with a better explanation
cheers,
rob