I did a RGB composit and I came out with this image from Saturn.

However I wonder how to avoid the mismatch on the border at the left of Saturn. I wanted to keep the Mimas with no color mismatch, so I couldn't help having this problem.

line them up separately. Line up Saturn, then create another color image where you get Mimas lined up with no mismatch that copy and paste that mimas, on top of the green Mimas in the image where you had Saturn lined up.