If you're using Televue Power mates then CA is usually not an issue, they ( Televue ) have very good optics, so again, Alex may be right with something not aligned properly in the optical train. As for the defringing function, yes, you're correct, I meant to say deringing. I've just had a haircut so I must have been thinking of that!
You can adjust the amount of deringing but you've probably given that a try as well. If that fails to remove the false colour, I will sometimes create a mask around the the planet in PS by using the Magic Wand tool with a tolerance of around 10, click in the black background, feather it with a value of around 50 then fill the selection with black. There's a bit of experimenting required with this method and you'll need to get yourself a copy of PS or similar image editing software. Good luck!