That is a gorgeous quilt! Looks daunting, but as long as you are careful and take your time it should be fairly straightforward as the designs are consistently repeated. Definitely would not be a quickie, at least not for me. But I certainly would like to attempt it - someday when I'm not trying to get whatever I'm doing done in a hurry.
As to your color changes, what sort of look are you wanting?
I would likely keep to the cool side of the spectrum and add more complimentary blues and greens. Of course I would also keep the purple just because I love it!
It would also be lovely done all from the warm side of the spectrum in reds, oranges and yellows. Completely different feel - more tropical sunset idea that way.