Bumping this up again since there's been some recent discussion of the Lady of the Green Kirtle's dress during the Maying/when she enchants Rilian.

I don't have any great ideas, but I just glanced through this thread and a couple of things struck me that I thought I'd share in case anyone else wanted to bounce off of them:
a) Adeona had suggested a kind of Celtic feel to her costumes, which I thought was rather interesting.
b) Several people suggested a gradient colour scheme, usually ranging from a light or pale green at the beginning to a dark green or brown at the end.
c) Someone also suggested the idea of LotGK's final costume silhouette changing throughout the final scenes; starting out in a more flowing or pouffy manner and then narrowing in until she transformed into a snake. I'm not sure how that would exactly look, but it sounds kind of cool.
